C programming session 02

Programming in C
Objectives

In this session, you will learn to:
Work with operators
Use loops
Use formatted input-output functions

Ver. 1.0 Slide 1 of 50

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
Logical Operators

Notations for logical operators in C are:
Operator Notation
OR ||
AND &&
NOT !
Operator precedence:
NOT (!) is evaluated before AND (&&), which is evaluated
before OR (||). Brackets () are used to change this order.


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
Practice: 2.1 (Contd.)

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

• 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:
– 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:
– True.
– If b is non-zero, it will determine the quotient of a and b. If b
equals zero, quotient is set to 0.
– Yes. Note that if b is non-zero, the test expression (b)
evaluates to true and hence quotient is set to (a/b).
– 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++.
5. True. i+1 is equivalent to 1+i.
4.

Microsoft Word
Document


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.

Microsoft Office
Word 97 - 2003 Document

2.

Microsoft Office


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:

Microsoft Office


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

In this session, you learned that:
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, ...);


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