Explain pointers and two-dimensional array in C language

Pointer is a variable that stores the address of another variable.

Features

• Pointer saves the memory space.

• Execution time of pointer is faster because of direct access to memory location.

• With the help of pointers, the memory is accessed efficiently, i.e., memory is allocated and deallocated dynamically.

• Pointers are used with data structures.

Pointers and two dimensional arrays

Memory allocation for a two-dimensional array is as follows −

int a[3] [3] = {1,2,3,4,5,6,7,8,9};

a[1] [2] = *(1234 + 1*3+2)
= *(1234 + 3+2)
= *(1234 + 5*4) // 4 is Scale factor
= * (1234+20)
= *(1254)
a[1] [2] = 6

Example

Following is the C program for pointers and two-dimensional array −

#include<stdio.h>
main ( ){
   int a[3] [3], i,j;
   int *p;
   clrscr ( );
   printf ("Enter elements of 2D array");
   for (i=0; i<3; i++){
      for (j=0; j<3; j++){
         scanf ("%d", &a[i] [j]);
      }
   }
   p = &a[0] [0];
   printf ("elements of 2d array are");
   for (i=0; i<3; i++){
      for (j=0; j<3; j++){
         printf ("%d \t", *(p+i*3+j));
      }
      printf ("
");
   }
   getch ( );
}

Output

When the above program is executed, it produces the following result −

enter elements of 2D array
1 2 3 4 5 6 7 8 9
Elements of 2D array are
1 2 3
4 5 6
7 8 9