Data Structures and Algorithms - Old Questions

11. What is dynamic memory allocation? How it is achieved for declaring two dimensional array? Explain.

The process of allocating memory at runtime is known as dynamic memory allocation. Library routines known as memory management functions are used for allocating and freeing memory during execution of a program. These functions are defined in stdlib.h header file.

A 2D array can be dynamically allocated in C using a single pointer. This means that a memory block of size row*column*dataTypeSize is allocated using malloc and pointer arithmetic can be used to access the matrix elements.

A program that demonstrates this is given as follows:

#include <stdio.h>
#include <stdlib.h> 
int main() {
   int row = 2, col = 3;
   int *arr = (int *)malloc(row * col * sizeof(int)); 
   int i, j;
   for (i = 0; i < row; i++)
      for (j = 0; j < col; j++)
         *(arr + i*col + j) = i + j;    
   printf("The matrix elements are:\\n");
   for (i = 0; i < row; i++) {
      for (j = 0; j < col; j++) {
         printf("%d ", *(arr + i*col + j)); 
      }
      printf("\\n");
   }
   free(arr); 
   return 0;
}