• A String is an array of character.
  • We can easily represent a string using one dimension array.
  • Similar to an array of integer that allows storing collection of integer values, we can also store string and represent string using an array of character.
  • We can think of a string as an array that can hold individual characters on different index.
  • A specific character in a string is accessed by an index.
  • Array index always starts from 0 and ends to n-1 that means first character of a string will be stored on index 0, second character on index 1 and so on. The last character will be ‘\0’ (NULL) into the string.
  • In C, array elements are allocated contiguous memory blocks.
  • String or character arrays can be represented by the following ways.
  1. Single -Dimension Arrays (String)
  2. Two- Dimension Arrays (Array of string)

Single -Dimension Arrays (String)

  • “An array of character is known as the one-dimensional character array or string”

Declaration and Initialization of String:

  • We can declare string using one dimension character array using the following syntax:
char string-var-name [size]  ;
  • string-var-name specifies name of the string to refer it. It can be any valid and meaningful name and it should follow all the naming convention rules.
  • Size defines number of maximum characters it can hold.
  • Size is defined inside the ‘[]’ brackets.
  • In C89, the size of an array must be specified using a constant expression. Thus, in C89, the size of an array is fixed at compile time. (C99 allows arrays whose sizes are determined at run time).
  • For example, to declare string called name  use this statement:
char name[6] = { ‘S’, ‘A’, ‘M’, ’M’, ’Y’, ’\0’   };
                        OR
char name [] = { ‘S’, ‘A’, ‘M’, ’M’, ’Y’, ’\0’   };
                        OR
char name [] = { “SAMMY” } ;   OR    char name [ ]  =  “SAMMY”  ;
  • Above string will be stored in memory as follow:

String Representation

  • Note that last character in string is ‘\0’ (NULL) character. It is used to identify end of the string
  • If we don’t specify null value at the end of the string, compiler will automatically insert null value at the end of the string.
Accessing string Elements:
  • We can access each character of string by using its index within square brackets along with string name.
  • For example, to access the first character of the string name, you can use name [0], for second element namd [1], and so on.
Dynamic initialization:
  • We can also initialize string at run time. It is referred to as dynamically initialization.
  • The following example uses for loop to initialize marks array from user at run time.
char name[15] ;
printf(“\n Enter Name :”);
scanf(“%s”, &name);    // OR  gets(name); (Need to include string.h)
  • Note that by default scanf() scans string only till it encounters space. As soon as it founds space, it stops scanning.
  • gets() can read string till it encounters null value so it is more suitable while reading long string.
  • The following program demonstrates reading string from user and displaying on the screen character by character.
/* Program to demostrate reading a string from the terminal. */

#include "stdio.h"
#include "string.h"

void main(void)
{
   char str[50];    /* this declares string 0f 50 cahracters*/
   int i=0;       
   clrscr();
             /* read string from the keyboard  */
   
   printf(“\n Enter String:”);
   gets(str); 
 
   while ( str[i]! = ‘\0’ )     /* display contents of str */
   {
      printf(“%c ”, i ) ;
      i++;
   }
}
  • The above program can be replaced with the following code fragment to read a string.
char ch;

/* this causes count to be overrun */

while ( ch = getchar() ! = ‘\0’)
    printf(“%c”, ch);

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