Explain dynamic memory allocation in C with an example

Problem

Find the sum of n numbers entered by user using dynamically allocated memory using C programming.

Solution

The Dynamic memory allocation enables the C programmers to allocate memory at runtime.

The different functions that we used to allocate memory dynamically at run time are −

• malloc () − allocates a block of memory in bytes at runtime.
• calloc () − allocating continuous blocks of memory at run time.
• realloc () − used for reduce (or) extend the allocated memory.
• free () − deallocates previously allocated memory space.

Following C program is to display the elements and calculate sum of n numbers.

Using dynamic memory allocation functions, we are trying to reduce the wastage of memory.

Example

 Live Demo

#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 : 
");    for(i=0;i<numofe;i++){       scanf("%d",p+i);       sum=sum+*(p+i);    }    printf("
The sum of elements is %d",sum);    free(p);//Erase first 2 memory locations//    printf("
Displaying the cleared out memory location : 
");    for(i=0;i<numofe;i++){       printf("%d
",p[i]);//Garbage values will be displayed//    } }

Output

Enter the number of elements : 5 Enter the elements : 23 34 12 34 56 The sum of elements is 159 Displaying the cleared out memory location : 12522624 0 12517712 0 56