Explain malloc function in C programming

Problem

Write a C program to display and add the elements using dynamic memory allocation functions.

Solution

In C, the library function malloc allocates a block of memory in bytes at runtime. It returns a void pointer, which points to the base address of allocated memory and it leaves the memory uninitialized.

Syntax

void *malloc (size in bytes)

For example,

• int *ptr;

  ptr = (int * ) malloc (1000);

• int *ptr;

  ptr = (int * ) malloc (n * sizeof (int));

Note − It returns NULL, if the memory is not free.

Example

#include<stdio.h>
#include<stdlib.h>
void main(){
   //Declaring variables and pointers,sum//
   int numofe,i,sum=0;
   int *p;
   //Reading number of elements from user//
   printf("Enter the number of elements : ");
   scanf("%d",&numofe);
   //Calling malloc() function//
   p=(int *)malloc(numofe*sizeof(int));
   /*Printing O/p - We have to use if statement because we have to check if memory has been successfully allocated/reserved or not*/
   if (p==NULL){
      printf("Memory not available");
      exit(0);
   }
   //Printing elements//
   printf("Enter the elements : \n");
   for(i=0;i<numofe;i++){
      scanf("%d",p+i);
      sum=sum+*(p+i);
   }
   printf("\nThe sum of elements is %d",sum);
   free(p);//Erase first 2 memory locations//
   printf("\nDisplaying the cleared out memory location : \n");
   for(i=0;i<numofe;i++){
      printf("%d\n",p[i]);//Garbage values will be displayed//
   }
}

Output

Enter the number of elements : 5
Enter the elements :
23
45
65
12
23

The sum of elements is 168
Displaying the cleared out memory location :
10753152
0
10748240
0
23