Introduction to String

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.

Single -Dimension Arrays (String)
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:

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);