C language (Collected By Dushmanta)

Programming in C
Objectives

In this session, you will learn to:
Identify the benefits and features of C language
Use the data types available in C language
Identify the structure of C functions
Use input-output functions
Use constructs

Ver. 1.0 Slide 1 of 53

Programming in C
Identifying the Benefits and Features of C Language

Ken Thompson developed a new language called B.
B language was interpreter-based, hence it was slow.
Dennis Ritchie modified B language and made it a
compiler-based language.
The modified compiler-based B language is named as C.


Programming in C
C as a Second and Third Generation Language

C language:
Possesses powerful low-level features of second generation
languages.
Provides loops and constructs available in third generation
languages.
Is very powerful and flexible.


Programming in C
Block Structured Language - An Advantage for Modular Programming

C language:
Offers all essentials of structured programming.
Has functions that work along with other user-developed
functions and can be used as building blocks for advanced
functions.
Offers only a handful of functions, which form the core of the
language.
Has rest of the functions available in libraries. These functions
are developed using the core functions.


Programming in C
Features of the C Language

The features that make C a widely-used language are:
Pointers: Allows reference to a memory location by a name.
Memory Allocation: Allows static as well as dynamic memory
allocation.
Recursion: Is a process in which a functions calls itself.
Bit Manipulation: Allows manipulation of data in its lowest form
of storage.


Programming in C
Using the Data Types Available in C language

The types of data structures provided by C can be classified
under the following categories:
Fundamental data types
Derived data types


Programming in C
Fundamental Data Types

Fundamental Data Types:
Are the data types at the lowest level.
Are used for actual data representation in the memory.
Are the base for other data types.
Have machine dependent storage requirement.
Are of the following three types:
char
int
float


Programming in C
Fundamental Data Types (Contd.)

The storage requirement for fundamental data types can be
represented with the help of the following table.

Data Number of bytes on a Minimum Maximum
32-byte machine
char 1 -128 127

int 4 -2^31 (2^31) - 1

float 4 6 digits of precision 6 digits of precision


Programming in C
Derived Data Types

Derived Data Types:
Are represented in memory as fundamental data type.
Some derived data types are:
short int
long int
double float


Programming in C
Derived Data Types (Contd.)

The storage requirement for derived data types can be
represented with the help of the following table.

Data Number of bytes Minimum Maximum
on a 32-byte
machine
short int 2 -2^15 (2^15) - 1

long int 4 -2^31 (2^31) - 1

double float 8 12 digits of precision 6 digits of
precision


Programming in C
Defining Data

The syntax for defining data is:
[data type] [variable name],...;

Declaration is done in the beginning of a function.
Definition for various data types is shown in the following
table.

Data definition Data type Memory defined Size (bytes) Value assigned
char a, c; char a 1 -
c 1 -
char a = 'Z'; char a 1 Z
int count; int count 4 -
int a, count =10; int a 4 -
count 4 10
float fnum; float fnum 4 -
float fnum1, float fnum1 4 -
fnum2 = 93.63; fnum2 4 93.63


Programming in C
Practice: 1.1

Write the appropriate definitions for defining the following
variables:
1. num to store integers.
2. chr to store a character and assign the character Z to it.
3. num to store a number and assign the value 8.93 to it.
4. i, j to store integers and assign the value 0 to j.


Programming in C
Practice: 1.1 (Contd.)

Solution:
1. int num;
2. char chr=‘Z‘;
3. float num = 8.93;
4. int i, j=0;


Programming in C
Defining Data (Contd.)

Defining Strings:
Syntax:
char (variable) [(number of bytes)];
Here number of bytes is one more than the number of
characters to store.
To define a memory location of 10 bytes or to store 9 valid
characters, the string will be defined as follows:
char string [10];


Programming in C
Practice: 1.2

Write the appropriate definitions for defining the following
strings:
1. addrs to store 30 characters.
2. head to store 14 characters.


Programming in C

Solution:
1. char addrs[31];
2. char head[15];


Programming in C
Identifying the Structure of C Functions

In C language, the functions can be categorized in the
following categories:
Single-level functions
Multiple-level functions


Programming in C
Single Level Functions

Single Level Functions:
Consider the following single-level function:
main()
{
/*print a message*/
printf("Welcome to C");
}
In the preceding function:
main(): Is the first function to be executed.
(): Are used for passing parameters to a function.
{}: Are used to mark the beginning and end of a function. These
are mandatory in all functions.
/* */: Is used for documenting various parts of a function.


Programming in C
Single Level Functions (Contd.)

Semicolon (;): Is used for marking the end of an executable
line.
printf(): Is a C function for printing (displaying) constant or
variable data.


Programming in C
Practice: 1.3

Identify any erroneous or missing component(s) in the
following functions:
1. man()
{
printf("This function seems to be okay")
}
2. man()
{
/*print a line*/
printf("This function is perfect―;
}


Programming in C

3. main()
}
printf("This has got to be right");
{
4. main()
{
This is a perfect comment line
printf("Is it okay?");
}


Programming in C

Solution:
1. man instead of main() and semi-colon missing at the end of
the printf() function.
2. mam instead of main() and ‘)’ missing at the end of the
printf() function.
3. ‘}’ instead of ‘{‘ for marking the beginning of the function and
‘{’ instead of ‘}‘ for marking the end of the function.
4. Comment line should be enclose between /* and */.


Programming in C
Multiple Level Functions

The following example shows functions at multiple
levels - one being called by another:
main ()
{
/* print a message */
printf ("Welcome to C.");
disp_msg ();
printf ("for good learning");
}
disp_msg ()
{
/* print another message */
printf ("All the best");
}


Programming in C
Multiple Level Functions (Contd.)

The output of the preceding program is:
Welcome to C. All the best for good learning.
In the preceding program:
main(): Is the first function to be executed.
disp_msg(): Is a programmer-defined function that can be
independently called by any other function.
(): Are used for passing values to functions, depending on
whether the receiving function is expecting any parameter.
Semicolon (;): Is used to terminate executable lines.


Programming in C
Practice: 1.4

Identify any erroneous or missing component(s) in the
following functions:
a. print_msg()
{ main();
printf(―bye‖);
}
main()
{ printf(―This is the main function‖);}
b. main()
{ /*call another function*/
dis_error();
}
disp_err();
{ printf(―Error in function‖);}


Programming in C

Solution:
a. main() is always the first function to be executed. Further
execution of the program depends on functions invoked from
main(). Here, after executing printf(), the program
terminates as no other function is invoked. The function
print_msg is not invoked, hence it is not executed.
b. The two functions, dis_error() and disp_error, are not
the same because the function names are different.


Programming in C
Using the Input-Output Functions

The C environment and the input and output operations are
shown in the following figure.

Standard Input Device (stdin) Standard Output Device (stdout)

C Environment

Standard Error Device (stderr)


Programming in C
Using the Input-Output Functions (Contd.)

These are assumed to be always linked to the C
environment:
stdin - refers to keyboard
stdin - refers to keyboard
stdout - refers to VDU
stderr - refers to VDU
Input and output takes place as a stream of characters.
Each device is linked to a buffer through which the flow of
characters takes place.
After an input operation from the standard input device, care
must be taken to clear input buffer.


Programming in C
Character-Based Input-Output Functions

Character-Based Input-Output Functions are:
getc()
putc()
getchar()
putchar()
The following example uses the getc() and putc()
functions:
# include < stdio.h>
/* function to accept and display a character*/
main ()
{char alph;
alph = getc (stdin); /* accept a character */
fflush (stdin); /* clear the stdin buffer*/
putc (alph, stdout); /* display a character*/
}


Programming in C
Character-Based Input-Output Functions (Contd.)

The following example uses the getchar() and
putchar() functions:
# include < stdio.h >
/* function to input and display a character using the
function getchar() */
main () {
char c;
c = getchar ();
fflush (stdin); /* clear the buffer */
putchar (c);
}


Programming in C
Practice: 1.5

1. Write a function to input a character and display the
character input twice.


Programming in C

Solution:


Programming in C
Practice: 1.6

1. Write a function to accept and store two characters in
different memory locations, and to display them one after
the other using the functions getchar() and
putchar().


Programming in C

Solution:
/* function to accept and display two characters*/
#include<stdio.h>
main()
{
char a, b;
a=getchar();
fflush(stdin);
b=getchar();
fflush(stdin);
putchar(a);
putchar(b);
}


Programming in C
String-Based Input-Output Functions

String-based input-output functions are:
gets()
puts()
The following example uses the gets() and puts()
functions:
# include < stdio.h >
/* function to accept and displaying */
main ()
{ char in_str {21}; /* display prompt */
puts ("Enter a String of max 20 characters");
gets (in_str); /* accept string */
fflush (stdin); /* clear the buffer */
puts (in_str); /* display input string */
}


Programming in C
Practice: 1.7

1. Write a function that prompts for and accepts a name with a
maximum of 25 characters, and displays the following
message.
Hello. How are you?
(name)
2. Write a function that prompts for a name (up to 20
characters) and address (up to 30 characters) and accepts
them one at a time. Finally, the name and address are
displayed in the following way.
Your name is:
(name)
Your address is:
(address)


Programming in C

Solution:


Programming in C
Using Constructs

There are two types of constructs in C language:
Conditional constructs
Loop constructs


Programming in C
Conditional Constructs

Conditional Constructs:
Requires relation operators as in other programming language
with a slight change in symbols used for relational operators.
The two types of conditional constructs in C are:
if..else construct
switch…case construct


Programming in C
Conditional Constructs (Contd.)

The Syntax of the if..else construct is as follows:
if (condition)
{
statement 1 ;

statement 2 ;
:
}
else
{
statement 1 ;
statement 2 ;
:
}


Programming in C
Practice: 1.8

1. Write a function that accepts one-character grade code, and
depending on what grade is input, display the HRA
percentage according to the following table.

Grade HRA %

A 45%

B 40%

C 30%

D 25%


Programming in C

Identify errors, if any, in the following function:
#include<stdio.h>
/*function to check if y or n is input*/
main()
{
char yn;
puts("Enter y or n for yes/no");
yn = getchar();
fflush(stdin);
if(yn=‘y‘)
puts("You entered y");
else if(yn=‗n')
puts("You entered n");
else
puts("Invalid input");
}


Programming in C

Solution:


Programming in C
Conditional Constructs (Contd.)

Syntax of switch…case construct:
switch (variable)
{
case 1 :
statement1 ;
break ;
case 2 :
statement 2 ;
:
:
break;
default :
statement
}


Programming in C
Practice: 1.9

Write a function to display the following menu and accept a
choice number. If an invalid choice is entered then an
appropriate error message must be displayed, else the
choice number entered must be displayed.
Menu
1. Create a directory
2. Delete a directory
3. Show a directory
4. Exit
Your choice:


Programming in C

Solution:


Programming in C
Loop Constructs

The two types of conditional constructs in C are:
while loop construct.
do..while construct.
The while loop construct has the following syntax:
while (condition in true)
{
statement 1 ; loop

statement 2 ; body
}
Used to iterate a set of instructions (the loop body) as long as
the specified condition is true.


Programming in C
Loop Constructs (Contd.)

The do..while loop construct:
The do..while loop is similar to the while loop, except that the
condition is checked after execution of the body.
The do..while loop is executed at least once.
The following figure shows the difference between the while loop
and the do...while loop.

while do while

False Execute
Evaluate
Body of
Condition
Loop
True
Execute False
Body of Evaluate
Loop Condition

True


Programming in C
Practice: 1.10

1. Write a function to accept characters from the keyboard until
the character ‘!’ is input, and to display whether the total
number of non-vowel characters entered is more than, less
than, or equal to the total number of vowels entered.


Programming in C

Solution:


Programming in C
Summary

In this session, you learned that:
C language was developed by Ken Thompson and Dennis
Ritchie.
C language combines the features of second and third
generation languages.
C language is a block structured language.
C language has various features that make it a widely-used
language. Some of the important features are:
Pointers
Memory Allocation
Recursion
Bit-manipulation


Programming in C
Summary (Contd.)

The types of data structures provided by C can be classified
under the following categories:
Fundamental data types: Include the data types, which are used
for actual data representation in the memory.
Derived data types: Are based on fundamental data types.
Fundamental data types:
char, int, and float
Some of the derived data types are:
short int, long int, and double float
Definition of memory for any data, both fundamental and
derived data types, is done in the following format:
[data type] [variable name],...;


Programming in C
Summary (Contd.)

In C language, the functions can be categorized in the
following categories:
Single-level functions
Multiple-level functions
For standard input-output operations, the C environment uses
stdin, stdout, and stderr as references for accessing the
devices.
There are two types of constructs in C language:
Conditional constructs
Loop constructs


Programming in C
Objectives

Work with operators
Use loops
Use formatted input-output functions


Programming in C
Working with Operators

An operator:
Is a symbol used to command the computer to do
mathematical or logical manipulations.
Operates on data and variables.
C has a rich set of operators, which can be classified into
following various categories:
Relational operators
Logical operators
Unary operators
Binary operators
Ternary operator
Compound assignment operators
Increment/Decrement operators


Programming in C
Practice: 2.1

Write a function that accepts either y or n only as input. For
any other character input, an appropriate error message
should be displayed and the input is accepted again.


Programming in C

Solution:
#include<stdio.h>
main()
{ char yn;
do {
puts(―Enter y/n (Yes/No)‖);
yn=getchar ();
fflush (stdin);
if(yn!=‘y‘ && yn!=‘n‘)
puts(―Invalid input‖);
}
while(yn!=‘y‘ && yn!=‘n‘);
}


Programming in C
Unary Operators

Unary Operators:
Operates on a single operand.
Prefixed to an integer constant.
Tells the compiler to reverse the sign by subtracting the value
(or variable) from zero.
Has the same effect as the – sign, which is used to indicate a
number less than zero, for example -12.


Programming in C
Practice: 2.2

Which of the following are valid?
1. valuea=-12; /* valuea is int* /
2. valuea = - valueb – 12 /* valuea and valueb
both are int */


Programming in C

Solution:
1. Valid
2. Valid


Programming in C
Binary Operators

Binary Operators:
Operate on two operands.
Are as follows:
+ (add)
- (subtract)
* (multiply)
/ (divide)
% (modulo)


Programming in C
Practice: 2.3

In the following set of statements:
char ch;
ch=‘S‘;
ch=ch+‘a‘-‗A‘; /*statement A*/
ch=ch+‘A‘-‗a‘; /*statement B*/
What will be the value of ch after:
1. Statement A is executed?
2. Statement B is executed?


Programming in C

Solution:
1. ch is equal to s. Note that ‘a’-‘A’ gives 32 after statement 1 is
executed.
2. ch is back to S after statement 2 is executed.


Programming in C
Binary Operators (Contd.)

There are some set or rules, if followed, would prevent
unexpected results, at the time of execution of programs:
Any operand of type char is converted to int.
All floats are converted to doubles.
If either operand is double, the other is converted to a
double, giving a double result.


Programming in C
Practice: 2.4

1. In which of the following assignments is there no loss of
data? (i is an int, f a float, and d a double)
i=d;
d=f;
f=d;
i=f+d;
d=i+f;
2. Is type casting necessary in the following example?
int i,j;
float f;
double d;
d=f+(float) i + j;


Programming in C

Solution:
1. a. Loss of data. int set equal to a double.
b. No loss of data. double set equal to a float.
c. Loss of data. float set equal to a double.
d. Loss of data. Right-hand result is a double while left-hand
side is just an int.
e. No loss of data. Right-hand result is a double and
left-hand side is also a double.
2. Not necessary. The ints will automatically be converted to
doubles (following the conversion of the float to a double).


Programming in C
Ternary Operator

Ternary Operator:
Is a shorthand method for writing if.else conditional
construct.
Helps in reducing lines of code.
Has the following form for the expression using the ternary
operator:
(test-expression) ? T-expression : F-expression;


Programming in C
Ternary Operator (Contd.)

Consider the following example:
if(condition)
{ Statements if condition is true }
else
{ Statements if condition is false }
Can be rewritten using the shorthand operator as follows:
larger_of_the_two = ( x > y ) ? x : y;


Programming in C
Practice: 2.5

1. State whether True or False:
In the general form of an expression that uses a ternary
operator, the test expression will be checked. If it is true, the T-
expression will be evaluated, otherwise the F-expression will be
evaluated.
2. What will the following statement do?
quotient = (b==0) ? 0 : (a/b); /*a, b, and
quotient are ints*/
3. Can the preceding statement be written as follows?
quotient = (b) ? (a/b) : 0;
4. What will the following statement do?
always_negative = (j>0) ? j : (-j);


Programming in C

Solution:
1. True.
2. If b is non-zero, it will determine the quotient of a and b. If b
equals zero, quotient is set to 0.
3. Yes. Note that if b is non-zero, the test expression (b)
evaluates to true and hence quotient is set to (a/b).
4. The variable always_negative will always take on a non-
negative value, i.e. it will be assigned the absolute value of j.
The name of the variable always_negative is just a red
herring. Remember that self-documenting variable names will
help in writing programs that are readable. Note the unary
operator (-j).


Programming in C
Compound Assignment Operators

Compound Assignment Operators:
Are useful especially when long variable names are used.
Has the following general form:
left-value op= right-expression;
Here op can be either + (add), - (subtract, * (multiply), /
(divide), and % (modulo).
a_very_long_identifier=a_very_long_identifier + 2;
It can be written as:
a_very_long_identifier += 2;


Programming in C
Increment / Decrement Operators

Increment / Decrement Operators:
Are used to increase or decrease the value of a variable by 1.
Has the following two forms:
The ++ (two plus symbols without a space), called the increment
operator while that in ++ before the variable is called the pre
increment operator and after the variable is called the post
increment operator.
The -- (two minus symbols without a space), called the decrement
operator while that in ++ before the variable is called the pre
decrement operator and after the variable is called the post
increment operator.


Programming in C
Increment / Decrement Operators (Contd.)

Consider the following code snippet:
total = sum++; /* statement A */
total = ++sum; /* statement B */
The first statement is equivalent to:
total = sum; sum = sum + 1;
While the second is the same as:
sum = sum + 1; total = sum;


Programming in C
Practice: 2.6

1. Consider the following code snippet:
int sum = 3, total = 5;
total = sum++;
total = ++sum; /*statement A */
total = sum—
total = --sum; /*statement B */
What will be the values of total and sum after:
a. statement A is executed?
b. statement B is executed?


Programming in C

The following statement:
for(i = 0; i< 100); i = i + 1)
{
Some statements
}
can be written as:

for (i = 0; i < 100; i++)
{
Some statements
}


Programming in C

The for statement in #2 can also be written as:
fori = 0; i < 100; ++i)/*Note: ++i and not i++*/
{
Some statements
}
4. Write a program, which reads in a year and reports on
whether it is a leap year or not (centuries should also be
considered).


Programming in C

Solution:
1. total=5, sum=5
total=3, sum=3
quite a complicated way of reducing total by 2.
2. True. i+1 is equivalent to i++.
3. True. i+1 is equivalent to 1+i.
4.


Programming in C
Using Loops

The while and do…while looping constructs are generally
used in situations where the number of execution of the loop
is not known.
The for loop construct is used when the number of
execution of the loop is known.


Programming in C
The for Loop Construct

The for loop construct:
Has three components in the loop control:
Initialization
Condition
Re-initialization (increment/decrement)
Has the following sequence of execution:
Initialization
Evaluation of loop condition
Body of loop
Re-initialization


Programming in C
The for Loop Construct (Contd.)

The sequence of execution of a complete for loop construct
is shown in the following figure.

INITIALIZATION

FALSE
EVALUATE
CONDITION

TRUE

BODY OF LOOP

REINITIALIZATION


Programming in C
The for Loop Construct (Contd.)

In a for loop construct:
Multiple initializations and/or multiple re- initializations, are
separated by commas.
Multiple conditions are specified using logical operators.


Programming in C
Practice: 2.7

1. Write a function to accept twenty characters from the
character set, and to display whether the number of lower-
case characters is greater than, less than, or equal to
number of upper-case characters. Display an error message
if the input is not an alphabet.
2. Modify the function to accept characters endlessly until the
character ! is input from keyboard.


Programming in C

Solution:
1.

2.


Programming in C
Controlling the Loop Execution

At times there is a need to exit from a loop before the loop
condition is re-evaluated after iteration.
To exit from loop control, break and continue statements
are used.


Programming in C
Practice: 2.8

Write a function, which accepts numbers until 0 is entered or
10 numbers have been accepted. The function prints the
total number of entries, the number of positive entries, and
the sum of all the positive numbers.


Programming in C

Solution:


Programming in C
Using Formatted Input-Output Functions

C provides the following functions for formatted input-output:
printf()
scanf()


Programming in C
Formatted Output

Syntax of the formatted output function printf() is:
printf (format, data1, data 2, ….);
printf(―%c‖, inp);
The character specified after % is called a conversion
character.
The conversion character allows one data type to be
converted to another type and printed.


Programming in C
Formatted Output (Contd.)

The conversion characters and their meanings are shown in
the following table.

Character Meaning

d the data is converted to decimal (integer)

c the data is taken as a character

s the data is a string and characters from
the string are printed until a NULL
character is reached
f the data is output as a double or float with
a default precision to 6


Programming in C
Practice: 2.9

What is the output of the statement:
printf(―Integer is: %d; Alphabet is: %cn‖,
inum, inp);
where inum contains 15 and inp contains Z.


Programming in C

Solution:
Integer is: 15; Alphabet is Z.


Programming in C
Formatted Input

The scanf() function is used for formatted input.
The syntax for the scanf() functions is as follows:
scanf (format, data1, data2……);
Here
format - The format-specification string
data1, data2 - Data names where the input data
is to be stored as per the
format-specification string


Programming in C
Formatted Input (Contd.)

The format-specification string in scanf() consists of:
Blanks, tabs, (also called white space characters).
New line which are ignored.
Conversion consisting of %, an optional number specification
specifying the width and a conversion character.
While accepting strings using scanf(), a space is
considered as a string terminator.


Programming in C
Practice: 2.10

Write a function to accept and display the element number
and the weight of a Proton. The element number is an
integer and weight is fractional.


Programming in C

Solution:
#include<stdio.h>
main()
{
int e_num;
float e_wt;
printf(―Enter the Element No. and Weight of a
Protonn‖);
scanf(―%d %f‖, &e_num, &e_wt);
fflush(stdin);
printf(―The Element No. is: ―, e_num);
printf(―The weight of a Proton is: %fn―,
e_wt);
}


Programming in C
Practice: 2.11

Write a function to input a string of continuous characters
with no white space as part of the input. The function should
assign the input to variables of the types specified in the
following table.
Position of character from Number of Type of argument to
start of string characters assign
1 2 int
3 4 float
7 2 char (string)
9 3 int

The function should also print out each of the assigned data
items in separate lines.


Programming in C
Practice: 2.11

Solution:
#include<stdio.h>
main()
{
int i,j;
char str[3];
float fnum;
printf(―Enter a string of 11 chrsn‖); /*why
11: because 11 is the total length of */
/*input.*/
scanf(―%2d %4f %2s %3d‖,&i, &fnum, str, &j);
fflush(stdin);
printf(―%2dn %4fn %2sn %3dn‖, i, fnum,
str, j);
}

Programming in C
Summary

An operator is a symbol that is used to command the computer
to do mathematical or logical manipulations.
The operators in C language are classified into the following
categories:
Logical operators
Unary operators
Binary operators
Ternary operator
Compound assignment operators
Increment/Decrement operators


Programming in C
Summary (Contd.)

The logical operators of C and their notations are as follows.

Operator Notation

OR ||

AND &&

NOT !

The unary operator prefixed to an integer constant or variable
tells the compiler to reverse the sign by subtracting the value
or variable from zero.
Binary operators in C language are + (add), - (subtract), *
(multiply), / (divide), and % (modulo).
Ternary operator offers a shorthand way of writing the
commonly used if…else construct.


Programming in C
Summary (Contd.)

The syntax for using the ternary operator is:
(test-expression) ? T-expression : F-expression;
Compound assignment operators simplify the statements.
Increment / Decrement operators are used to
increment/decrement a variable by 1.
A for loop is used when the number of execution of the loop
is known.
The components of a for loop construct are:
initialization
loop condition
reinitialization (increment/decrement)


Programming in C
Summary (Contd.)

The sequence of execution of a complete for loop is:
initialization
evaluation of the loop condition
the body of the loop
reinitialization
The break and continue statements are used to exit from
loop control.
The break statement is used to exit from all loop constructs
(while, do...while, and for) and switch...case
statements.
The continue statement is used to skip all subsequent
instructions and brings the control back to the loop.
The function printf() is used for formatted output to
standard output based on a format specification.


Programming in C
Summary (Contd.)

The syntax of the function printf() is:
printf(format, datal, data 2,,..);
The function scanf() is used for formatted input from
standard input and provides many of the conversion facilities of
the function printf().
The syntax of the function scanf() is:
scanf (format, datal, data2, ...);


Programming in C
Objectives

In this session, you will do the practice questions of Chapter
1 and Chapter 2.


Programming in C
Chapter 1

1. Write a function to accept a character and display it 40
times.
2. Write a function that accepts a number from 0 to 9, along
with a string. The string should then be displayed the
number of times specified.


Programming in C
Chapter 2

1. Write a for loop, which will produce the following output
(Hint: use two nested for loops):
1
22
333
4444
55555
2. Create a C program, which calculates the triangular number
of the user’s request, read from the keyboard using scanf().
A triangular number is the sum of the preceding
numbers, so the triangular number 7 has the value of
7+6+5+4+3+2+1 (same as a factorial in mathematics, for
example, factorial of 7 ---- !7).


Programming in C
Chapter 2

3. Create a C program to check whether the number entered
by user is even or odd.


Programming in C
Objectives

Work with arrays
Appreciate preprocessor directives


Programming in C
Working with Arrays

Arrays:
Are a group of similar objects.
Can be defined as a contiguous area in memory.
Can be referred to by a common name.
Has a unique identifier for each element, called as a subscript
or an index.
Can be categorized as:
One-dimensional/Single-dimensional arrays
Multidimensional arrays


Programming in C
One-Dimensional Arrays

The syntax for declaring a one-dimensional array is:
type arrayname[n];
For Example:
char string [11];
Defines a character array named string to store 10
characters.
string[0] to string[9] are for valid characters.
string[10] for the string-terminator character, 0 (NULL).
Similarly:
int numbers [11];
Defines an integer type array called numbers to store 11
integers.
Integers are stored in numbers[0] to numbers[10].


Programming in C
Practice: 3.1

1. Write the array definition statements for storing the following
data:
a. Ten amounts with paisa.
b. Five ages to be stored in years and six non-fractional
quantities.
c. A thirty character long name.


Programming in C

Solution:
a. float fnum[10];
b. int age[5], qty[6];
c. char name[31];


Programming in C
One-Dimensional Arrays (Contd.)

Initializing Arrays:
An array can be initialized, when declared.
Initialization at the time of declaration is possible only outside a
function unless it is declared static.
Direct initialization is possible in the following ways:
char strl[7]={‗E‘,‘X‘,‘O‘,‘D‘,‘U‘,‘S‘,‘0‘};
char str2[7]={"EXODUS"};
In the first case, individual elements have been moved into the
array. Therefore, it is essential that the string terminator be
specified explicitly. While in the second case, the string
terminator gets attached automatically because a string has
been assigned.


Programming in C
Practice: 3.2

1. Write a function that stores the alphabets A to Z in an array
by applying arithmetic on ASCII codes, given that the ASCII
code of character A is 65. The function should display the
string also.
2. In a file-delete utility program for 256 files the user response
to whether a file is to be deleted or not is to be stored in an
array as Y for yes and N for no for all files. By default the
user response should be N for all files. Write a function that
sets up an array and accepts user-responses.


Programming in C

Solution:


Programming in C

Array elements:
Are referenced by using subscripts.
Are integers, therefore array manipulation is possible through
the use of variables.


Programming in C
Practice: 3.3

1. Write a function to convert a character string into
lower-case.
2. Write a function to compare two strings and to print the
larger one. The strings may be compared in terms of ASCII
code of each character in the strings.


Programming in C

Solution:


Programming in C
Practice: 3.4

1. Write a function to accept up to 25 numbers and to display
the highest and lowest numbers along with all the numbers.


Programming in C

Solution:


Programming in C

Array Addressing:
To arrive at a particular element, the following formula is
applied:
Starting address + ( Offset number * Scaling
factor) of the array
Here,
Scaling factor is the number of bytes of storage space required
by the specific data type.
Offset number * Scaling factor gives the number of bytes
to be added to the starting address of the array to get to a desired
element.


Programming in C
Practice: 3.5

1. Write a program in C to extract a substring from a specified
position containing a specified number of characters from
an input string.


Programming in C

Solution:


Programming in C
Multidimensional Arrays

C also supports multidimensional arrays.
A two-dimensional array is the simplest form of the
multidimensional array.
A two-dimensional array is an array of one-dimensional
arrays.
A two-dimensional array is also known as a two-d array.
A two-d array is declared as follows:
type arrayname[Row][Col];
Rules for initializing a two-d array are same as that of a
one-dimensional array.
The row subscript may be left blank for a more flexible
declaration.


Programming in C
Practice: 3.6

If the number of salesmen is 5, then the declaration of the
two-dimensional array and its initialization to zero would be:
int s_p_array [5][4] = {
{0,0,0,0,0},
{0,0,0,0,0},
{0,0,0,0,0},
{0,0,0,0,0},
};


Programming in C

Solution:
1. False. Note that since there are 5 salesman with 4
products, there should be 5 sets of {}, each containing four
zeroes. The correct initialization is:
int s_p_array [5][4] = {
{0,0,0,0},
{0,0,0,0},
{0,0,0,0},
{0,0,0,0},
{0,0,0,0},
};


Programming in C
Multidimensional Arrays (Contd.)

Two-Dimensional Character Arrays:
Are typically used to create an array of strings.
Use two subscripts, one for row and the other for column.
Are declared as:
char err_msg [row] [col];
Can be initialized at the time of declaration.


Programming in C
Practice: 3.7

1. Based on the books array, predict the output of the following
commands:
a. printf(―%c‖, books[2][5]);
b. printf(―%s‖,books[3]);
c. printf(―%d‖,books[4][7]);


Programming in C

Solution:
a. M
b. Birds, Beasts, and Relatives
c. 97


Programming in C
Practice: 3.8

1. Write the program segment to calculate the class average
across students in each subject.
2. Assume that the data exists in the arrays and averages
have been calculated. Write program segments, which will
allow the user to query on the arrays to:
a. Display Student Names and Average Marks.
b. Display Subjects and Class Averages.


Programming in C

c. Display Marks of a specific Student in a specific Subject.
d. Display Subject wise marks of all students whose average is
above 80.
For each option the following action needs to be taken.

OPTION ACTION
a. Display each student's name along with his average marks.
b. Display each subject along with class average on the subject.
c. Display list of students and list of subjects. Allow the user to
choose one from each. Based on the numbers chosen, display
the appropriate marks. Remember, subscripting in C starts from
zero.
d. Check the average of each student. Wherever average exceeds
80, display the student name and the subject name and marks
in each subject.


Programming in C

Solution:


Programming in C
Appreciating Preprocessor Directives

Preprocessor directives:
Are instructions to the compiler in the source code of a C
program.
Are not actually a part of the C language.
Expand the scope of the C programming environment.
Begin with a #.
#include is also a preprocessor directive.
#include instructs the compiler to include the specified
source file into the one which contains the #include
directive.
#define defines an identifier and a string constant that will
be substituted for the identifier each time it is encountered in
the file.


Programming in C
Appreciating Preprocessor Directives (Contd.)

It helps in reducing the chances of inconsistency within the
program and also makes the program easy to modify.
Consider the following macro definition:
#define TRUE 1
No semicolon is required after the statement.
Every time the compiler encounters the string TRUE in the
program, it substitutes it with the value 1.
No text substitution will occur if the identifier is enclosed
within quotes.


Programming in C
Summary

An array can be defined as a contiguous area in memory,
which can be referred to by a common name.
In C, arrays can be categorized as:
One-dimensional/Single-dimensional arrays
Multidimensional arrays
The syntax for declaring a one-dimensional array is as follows:
type arrayname[n];
Array elements are referenced by using subscripts.
The last element in a character array is reserved to store the
string terminator character 0 (NULL).
An array can be initialized, when declared, by specifying the
values of some or all of its elements.
Initialization can also be done inside the function, after the
array has been declared, by accepting the values.


Programming in C
Summary (Contd.)

To arrive at the particular element, the following formula is
applied:
Starting address + ( Offset number * Scaling
factor) of the array
C supports multidimensional arrays.
The simplest form of the multidimensional array is the
two-dimensional (two-d) array.
The general form of declaration of the two-d array would be:
type arrayname[x][y];
Two-dimensional integer arrays are very much like
one-dimensional integer arrays, the only difference being that
two-dimensional arrays have two indices.
Initialization of two-dimensional arrays can be done at the time
of declaration itself.
A better way to initialize a two-dimensional array is using the
for statement.

Programming in C
Summary (Contd.)

Two-dimensional character arrays are declared in the same
way as two-dimensional integer arrays:
The first index specifies the number of strings.
The second index specifies the length of the longest string plus
one.
Initialization can be done along with declaration, if done
outside main().
Preprocessor directives are not actually a part of the C
language; they expand the scope of the C programming
environment.
The preprocessor directives normally begin with a #.
#include is also a preprocessor directive. It instructs the
compiler to include the specified source file into the one which
contains the #include directive.


Programming in C
Summary (Contd.)

The #define statement can be used to declare a variable with
a constant value throughout the program. It helps in:
Reducing the chances of inconsistency within the program.
Making modification easier, as the value has to be changed only
at one place.


Programming in C
Objectives

Declare and manipulate pointers
Use pointers to manipulate character arrays


Programming in C
Declaring and Manipulating Pointers

Every stored data item occupies one or more contiguous
memory cells.
Every cell in the memory has a unique address.
Any reference to a variable, declared in memory, accesses
the variable through the address of memory location.
Pointers are variables, which contain the addresses of other
variables (of any data type) in memory.


Programming in C
Declaring Pointers

A pointer variable must be declared before use in a
program.
A pointer variable is declared preceded by an asterisk.
The declaration:
int *ptr; /* ptr is pointing to an int */
Indicates that ptr is a pointer to an integer variable.
An uninitialized pointer may potentially point to any area of
the memory and can cause a program to crash.
A pointer can be initialized as follows:
ptr= &x;
In the preceding initialization, the pointer ptr is pointing to x.


Programming in C
Practice: 4.1

1. In the following declaration:
float *ptr_to_float;
The pointer variable ptr_to_float is pointing to a
variable of type ____________.
2. Is the following declaration valid?
*ptr_to_something;
An integer is declared In the following declaration:
int *ptr_to_int;
4. Is the following declaration valid?
int some_int, *ptr_to_int;


Programming in C

Solution:
1. float
2. No. When a pointer variable is being declared, the type of
variable to which it is pointing to (int, float, or char)
should also be indicated.
3. False. A pointer to an integer is being declared and not an
integer.
4. Yes. It is okay to club declaration of a certain type along with
pointers to the same type.


Programming in C
Manipulating Pointers

Pointers can be manipulated like variables.
The unary operator * gives value of the variable a pointer is
pointing to.
The unary operator * is also termed as the indirection
operator.
The indirection operator can be used only on pointers.


Programming in C
Practice: 4.2

1. The symbol _________ is used to obtain the address of a
variable while the symbol__________ is used to obtain the
value of the variable to which a pointer is pointing to.
2. With the following declarations:
int x, y, *ptr;
Which of the following are meaningful assignments?
a. x = y;
b. y=*ptr;
c. x = ptr;
d. x = &.ptr;
e. ptr = &x;
f. x = &y;


Programming in C

3. Consider the following sequence of statements and
complete the partially-filled table:
int x, y, *ptrl, *ptr2;
x = 65;
y = 89;
ptr1 = &x; /*ptrl points to x */
ptr2 = &y/; /* ptr2 points to y */
x = *ptr1; /* statement A*)
ptr1 = ptr2: /* statement B */
x = *ptr1; /* statement C*/
After statement &x x &y y ptr1 ptr2
A 1006 1018
B
C


Programming in C

4. What is the output of the following sequence of statements:
int x, y, temp,*ptrl, *ptr2; /* declare */
x = 23;
y = 37;
ptrl = &x;/* ptrl points to x */
ptr2 = &y;/* ptr2 points to y */
temp = *ptrl;
*ptr1 = *ptr2;
*ptr2 = temp;
printf(―x is %d while y is %d‖, x, y);


Programming in C

Solution:


Programming in C
Pointer Arithmetic

Pointer Arithmetic:
Arithmetic operations can be performed on pointers.
Therefore, it is essential to declare a pointer as pointing to a
certain datatype so that when the pointer is incremented or
decremented, it moves by the appropriate number of bytes.
Consider the following statement:
ptr++;
It does not necessarily mean that ptr now points to the next
memory location. The memory location it will point to will
depend upon the datatype to which the pointer points.
May be initialized when declared if done outside main().
#include <stdio.h>
char movie[]= ―Jurassic Park‖;
main() {
char *ptr;

Programming in C
Pointer Arithmetic (Contd.)

#include <stdio.h>
char movie[]= ―Jurassic Park‖;
main() {
char *ptr;
ptr=movie;
printf(―%s‖, movie); /* output: Jurassic Park */
printf(―%s‖,ptr); /* output: Jurassic Park */
ptr++;
printf(―%s‖,movie); /* output: Jurassic Park */
printf(―%s",prr); /* output: urassic Park */
ptr++;
printf(―%s‖,movie); /* output; Jurassic Park */
printf(―%s‖,ptr); /* output: rassic Park */
/* Note that the incrementing of the pointer ptr
does not in any way affect the pointer movie */
}


Programming in C
Practice: 4.3

1. Consider the following code snippet:
#include <stdio.h>
int one_d[] = {l,2,3};
main(){
int *ptr;
ptr = one_d;
ptr +=3; /* statement A*/
printf(―%dn‖, *ptr); /*statement B */
}
a. After statement A is executed, the new address of ptr will be
____ bytes more than the old address.
b. State whether True or False:
The statement B will print 3.


Programming in C

Solution:
a. 12 ( Size of integer = 4*3)
b. False. Note that ptr is now pointing past the one-d array.
So, whatever is stored (junk or some value) at this address is
printed out. Again, note the dangers of arbitrary assignments
to pointer variables.


Programming in C
Using Pointers to Manipulate Character Arrays

Array name contains the address of the first element of the
array.
A pointer is a variable, which can store the address of another
variable.
It can be said that an array name is a pointer. Therefore, a
pointer can be used to manipulate an array.


Programming in C
One-Dimensional Arrays and Pointers

One-Dimensional Arrays and Pointers:
#include <stdio.h>
char str[13]={―Jiggerypokry‖};
char strl[]={ ―Magic‖};
main() {
char *ptr;
printf(―We are playing around with %s", str);
/* Output: We are playing around with Jiggerypokry*/
ptr=str ; /* ptr now points to whatever str is
pointing to */
printf(―We are playing around with %s" ,ptr);
/* Output: We are playing around with Jiggerypokry */
}


Programming in C
One-Dimensional Arrays and Pointers (Contd.)

In the preceding example the statement:
ptr=str;
Gives the impression that the two pointers are equal. However,
there is a very subtle difference between str and ptr. str is a
static pointer, which means that the address contained in str
cannot be changed. While ptr is a dynamic pointer. The address
in ptr can be changed.


Programming in C
Practice: 4.4

1. Given the declaration:
char some_string [10];
some_string points to _________.
In the following declaration, the pointer err_msg contains a
valid address:
char *err_msg = ―Some error message‖;
Consider the following declaration:
char *err_msg = ―Some error message‖;
It is more flexible than the following declaration:
char err_msg[19]=‖Some error message‖;


Programming in C

Solution:
1. some_string [0]
2. True
3. True. Note that one does not have to count the size of the
error message in the first declaration.


Programming in C
Two-Dimensional Arrays and Pointers

Two-dimensional arrays can be used to manipulate multiple
strings at a time.
String manipulation can also be done by using the array of
pointers, as shown in the following example:
char *things[6]; /* declaring an array of 6
pointers to char */
things[0]=‖Raindrops on roses‖;
things[1]=‖And Whiskers on kettles‖;
things[2]=‖Bright copper kettles‖;
things[3]=‖And warm woolen mittens‖;
things[4]=‖Brown paper packages tied up with
strings‖;
things[5]=‖These are a few of my favorite
things‖;


Programming in C
Two-Dimensional Arrays and Pointers (Contd.)

The third line of the song can be printed by the following
statement:
printf(―%s‖, things[2]);
/*Output: Bright copper kettles */


Programming in C
Practice: 4.5

While declaring two-dimensional character arrays using
pointers, yon do not have to go through the tedium of
counting the number of characters in the longest string.
2. Given the following error messages:
All's well
File not found
No read permission for file
Insufficient memory
No write permission for file
Write a program to print all the error messages on
screen, using pointers to array.


Programming in C

Solution:
1. True. New strings can be typed straight away within the {}. As
in:
char *err_msg_msg[]= {
―All's well‖,
―File not found‖,
―No read permission for file‖,
―Insufficient memory‖,
―No write permission for file‖
};
The number of strings will define the size of the array.


Programming in C

2. The program is:
# include<stdio.h>
# define ERRORS 5
char *err_msg[]= { /*Note the missing index*/
―All's well‖,
―File not found‖,
―No read permission for file‖,
―Insufficient memory‖,
―No write permission for file‖ };
main() {
int err_no;
for ( err_no = 0; err_no < ERRORS; err_no++ ) {
printf ( ―nError message %d is : %sn‖, err_no +
1, err_msg[err_no]); } }


Programming in C
Two-Dimensional Arrays and Pointers (Contd.)

Consider the following two-d array declaration:
int num[3][4]= {
{3, 6, 9, 12},
{15, 25, 30, 35},
{66, 77, 88, 99}
};
This statement actually declares an array of 3 pointers (constant)
num[0], num[l], and num[2] each containing the address of
the first element of three single-dimensional arrays.
The name of the array, num, contains the address of the first
element of the array of pointers (the address of num[0]).
Here,
*num is equal to num[0] because num[0] points to num[0][0].
*(*num) will give the value 3.
*num is equal to num[0].


Programming in C
String-Handling Functions Using Pointers

Pointers can be used to write string-handling functions.
Consider the following examples:
/* function to calculate length of a string*/
#include <stdio.h>
main() {
char *ptr, str[20];
int size=0;
printf(―nEnter string:‖);
gets(str);
fflush(stdin);
for(ptr=str ; *ptr != '0'; ptr++) {
size++;
} printf(―String length is %d‖, size);
}


Programming in C
Using Pointers to Manipulate Character Arrays (Contd.)

/*function to check for a palindrome */
# include <stdio.h>
main() {
char str[50],*ptr,*lptr;
printf(―nEnter string :‖);
gets(str); fflush(stdin);
for(lptr=str; *lptr !=‘0'; lptr++); /*reach
the string terminator */
lptr--; /*position on the last character */
for(ptr=str; ptr<=lptr; lptr--,ptr++) {
if(*ptr != *lptr)
break;}
if(ptr>lptr)
printf(―%s is a palindrome‖ );
else
printf(―%s is not a palindrome");
}

Programming in C
Summary

A pointer is a variable, which contains the address of some
other variable in memory.
A pointer may point to a variable of any data type.
A pointer can point to any portion of the memory.
A pointer variable is declared as:
datatype *<pointer variable name>
A pointer variable is initialized as:
pointer variable name> = &<variable name to which
the pointer will point to>
The & returns the address of the variable.
The * before a pointer name gives the value of the variable to
which it is pointing.


Programming in C
Summary (Contd.)

Pointers can also be subjected to arithmetic.
Incrementing a pointer by 1 makes it point to a memory
location given by the formula:
New address = Old address + Scaling factor
One-dimensional character arrays can be declared by
declaring a pointer and initializing it.
The name of a character array is actually a pointer to the first
element of the array.
Two-dimensional character arrays can also be declared by
using pointers.


Programming in C
Objectives

Implement modular approach in C programs
Use library functions for string manipulation
Work with data storage types


Programming in C
Implementing Modular Approach in C Programs

Functions are the building blocks of C.
Every C program must consist of at least one function,
main().
The main() function is the entry point of a C program.


Programming in C
Advantages of Functions

Functions:
Allow reusability of code and structuring of programs.
Provide programmers a convenient way of designing
programs.


Programming in C
Parameters of Functions

A parameter:
Is the data that the function must receive when called from
another function.
May or may not be present in a function.
Of a user-defined function is declared outside the {} of that
function.


Programming in C
Practice: 5.1

1. From the following program, identify the functions invoked
from main(), and state which functions have parameters.
Also state the parameters.


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