Review of C.pptx

Review of C
Strings, Arrays and Pointers

C Orientation
• Created in 1972 to write operating systems (Unix
in particular)
– By Dennis Ritchie
– Bell Labs
• Evolved from B
• Can be portable to other hardware
• Built for performance and memory management
– operating systems, embedded systems, real-
time systems, communication systems

What are the advantages of C?
• Portable: allows code to run on different computers and operating
systems without making any change.
• Efficient: It is a general-purpose programming language.
Therefore it works efficiently.
• Case-sensitive: You need to be very careful while writing the code
as it treats lowercase and uppercase letter differently.
• Memory Manipulation and allocation: allows allocating the
memory dynamically.
• Middle-level language: It merges the features of both low level
and high-level languages in itself.

What are the disadvantages of C?
• C language is devoid with the terminology and the concept of
OOPS which is a very popular and an important concept these
days among all high-level programming language.
• No Strict type checking possible.
• No checks for runtime
• It doesn’t give us the provision of having a namespace.
• It also doesn’t have the concept of the constructor as well as a
destructor.

A First Program
#include <stdio.h>
int main(void)
{
printf("This is my first C program.n");
return(0);
}
statements
header
open and close braces mark
the beginning and end
makes input
and output available
to us

A First Program – What Does It Do?
printf("This is my first C program.n");
return(0);
Prints the message
This is my first C program.
Ends the program Ends the line

C Program Phases
• Editor - code by programmer
• Compiling using gcc:
– Preprocess – expand the programmer’s code
– Compiler – create machine code for each file
– Linker – links with libraries and all compiled
objects to make executable
• Running the executable:
– Loader – puts the program in memory to run it
– CPU – runs the program instructions

Copyright © Pearson, Inc. 2013. All
Rights Reserved.

Using variables
#include <stdio.h>
int main(void)
{
int sum, value1, value2, value3;
float average;
value1 = 2;
value2 = 4;
value3 = 6;
sum = 2 + 4 + 6;
average = sum / 3;
printf("The average of %d , %d, %d is %fn",
value1, value2, value3, average);
return(0);
}
Print a float value from the
rest of the parameter list

A program that uses a character variable
#include <stdio.h>
/* A very polite program that greets you by name */
int main(void)
{
char name[25];
/* Ask the user his/her name */
printf("What is your name ? ");
scanf("%s", name);
/* Greet the user */
printf("Glad to meet you, %sn.", name);
return(0);
}

Features so far
• Include
• Variable types: int, float, char
• Read using scanf
– requires & for address of variable being read
• Print using printf
• Format strings: %f (float), %d (int), %u
(unsigned int), %c (char), %s (character array)
• Comments /*.. */ or //

Array - Review
• Array – a set of elements all of the same type
stored contiguously in memory – e.g.,
– int A[25]; // 25 integers
– struct Str B[15]; /* 15 objects of
type struct Str */
– double C[]; /* indeterminate #
of doubles */
• Pointer – a variable whose value is the
location of some other object
– float *p; // pointer to a float

Array - Review
int A[25]; // 25 integers
• Type of A[i] is int (for all i).
• Type of A is int *
• I.e., pointer to int

15
Strings in C
• Definition:– A string is a character array ending in
'0' — i.e.,
– char s[256];
– char t[] = "This is an initialized string!";
– char *u = "This is another string!";
• String constants are in double quotes
• May contain any characters
• Including " and '
• String constants may not span lines
• However, they may be concatenated — e.g.,
"Hello, " "World!n" is the same as "Hello, World!n"

16
Strings in C (continued)
• Let
– char *u = "This is another string!";
• Then
– u[0] == 'T'
u[1] == 'h'
u[2] == 'i'
…
u[21] == 'g'
u[22] == '!'
u[23] == '0'

Strings, Arrays, and Pointers CS-2303, C-Term 2010 17
Support for Strings in C
• Most string manipulation is done through functions
in <string.h>
• String functions depend upon final '0'
• So you don’t have to count the characters!
• Examples:–
– int strlen(char *s) – returns length of string
• Excluding final '0'
– char* strcpy(char *s, char *ct) – Copies string ct to
string s, return s
• s must be big enough to hold contents of ct
• ct may be smaller than s

18
Support for Strings in C (continued)
• Examples (continued):–
– int strcmp(char *s, char *t)
• lexically compares s and t, returns <0 if s < t, >0 if
s > t, zero if s and t are identical
– D&D §8.6, K&R p. 106
– char* strcat(char *s, char *ct)
• Concatenates string ct to onto end of string s, returns s
• s must be big enough to hold contents of both strings!
• Other string functions
– strchr(), strrchr(), strspn(), strcspn()
strpbrk(), strstr(), strtok(), …

String - Review
• string.h functions for string manipulation
– String in C – null terminated array of characters
char *s1 = “String1”;
char buff[10];
strcpy(buff, s1);
printf(“%s %dn”, s1, strlen(s1)); // String1 7
buff[3] = ‘0’;
printf(“%s %dn”, s1, strlen(s1)); // Str 3
strcat(buff, “ange”); // buff is Strange
strcmp(s1, “String2”) <= 0 // true (s1 <= “String2”)

Pointers - Review
A pointer is a reference to another variable (memory
location) in a program
– Used to change variables inside a function (reference
parameters)
– Used to remember a particular member of a group (such
as an array)
– Used in dynamic (on-the-fly) memory allocation (especially
of arrays)
– Used in building complex data structures (linked lists,
stacks, queues, trees, etc.)

Pointer - Review
Variables are allocated at addresses in computer memory
(address depends on computer/operating system)
Name of the variable is a reference to that memory address
A pointer variable contains a representation of an address of
another variable (P is a pointer variable in the following):
101
V P
Name
Abstract
Representation
Concrete
Representation
Address
4 bytes for
int value 101
4 bytes for
mem address v
v (some value) p (some value)
int V = 101;
int *P = &V;

Pointer Variable Definition
Basic syntax: Type *Name
Examples:
int *P; /* P is var that can point to an int var */
float *Q; /* Q is a float pointer */
char *R; /* R is a char pointer */
Complex example:
int *AP[5]; /* AP is an array of 5 pointers to ints */
– more on how to read complex declarations later

Sample Program
#include <stdio.h>
int main()
{
int x, y, *a, *b, temp;
printf("Enter the value of x and yn");
scanf("%d%d", &x, &y);
printf("Before Swappingnx = %dny = %dn", x, y);
a = &x;
b = &y;
temp = *b;
*b = *a;
*a = temp;
printf("After Swappingnx = %dny = %dn", x, y);
return 0;
}

Review of C.pptx

Recommandé

Recommandé

Contenu connexe

Similaire à Review of C.pptx

Similaire à Review of C.pptx (20)

Dernier

Dernier (20)

Review of C.pptx