What is the purpose of realloc( )

The function realloc () is used to resize the memory allocated earlier by function malloc () to a new size given by the second parameter of the function. The function realloc(ptr,n) uses two arguments.the first argument ptr is a pointer to a block of memory for which the size is to be altered. The second argument n specifies the new size. The size may be increased or decreased.

If n is greater than the old size and if sufficient space is not available subsequent to the old region, the function realloc( ) may create a new region and all the old data are moved to the new region.

Illustrates malloc() and realloc ().

#include <stdio.h> 
  
 #include<stdlib.h> 
  
 int main () 
  
 { 
  
   int a= 0, n, m, i, j,k =0; 
  
   int* Array; 
  
   clrscr(); 
  
   printf("Enter the number of elements of Array."); 
  
   scanf("%d", &n ); 
  
   Array= (int*) malloc( n* sizeof(int) ); 
  
   if( Array== NULL) 
  
   { 
  
      printf("Error. Out of memory.\n"); 
  
      exit(0); 
  
   } 
  
   printf("Enter the %d elements of Array:", n); 
  
    for ( i =0; i<n; i++) 
  
     scanf("%d",&Array[i]); 
  
     for( j =0;j<n; j++) 
  
       printf("Array[%d] = %d\n", j, *(Array+j)); 
  
       printf("Enter the number of elements of extended array."); 
  
       scanf("%d", &m); 
  
       Array= realloc(Array, m); 
  
       if( Array== NULL) 
  
        { 
  
          printf("realloc has failed.\n"); 
  
          exit(0); 
  
        } 
  
        printf("Enter values of %d additional elements of array.", m-n); 
  
        for (k= n ; k<m; k++) 
  
          scanf("%d", &Array[k]); 
  
           for( a =0;a<m; a++) 
  
           printf("Array[%d] = %d\n", a, *(Array+ a)); 
  
           return 0; 
  
 }