Free

Any dynamically located memory, remains allocated till the time that program is available. To deallocate the memory we need to explicitly deallocate the memory by using function free()

Example malloc,realloc,free :

#include<stdio.h>
#include<conio.h>
#include<stdlib.h>

void main()
{
    int n;

    printf(“Enter size of array”);
    scanf(“%d”, &n);

    int *a = (int)malloc(n*sizeOf(int)); //dynamically allocated array
    //if we donot initialize the values in the array, then by default the malloc will assign garbage values in the block of memory
    //so if we comment the below for loop then it will print garbage values

    for(int i = 0; i < n; i++)
    {
        a[i]=i+1;//assigning values as 1,2,3..n;
    }

    //if we use free() function below, to free the memory space then free() function will erase all the data from memory.

    //Free(a);// so better not to use free() here

    //now this below for loop will print garbage values because the free() has removed all data from memory.
    //To resize the memory block: we have memory block to store n elements in an array, and we want to double the size of array or want to reduce the size, so for this we can use realloc().

    int *b = (int )realloc(a,2*n*sizeof(int));//this will allocate double the size of previous block.
    //after realloc(), it will create new memory block of size 2n and copy the values of previous block of memory values into the new memory block b.
    //so previous values for n =2,were a[0]=1 and a[1]=2, then after realloc, the block of memory will be 2*n=2*2=4
    //so if we print the values that is there in the new block b as


    for(int i = 0; i < n; i++)
    {
        printf(“%d ”,b[i]);
        //n=2,so new size of memory block is 2*2=4,this will print values as “1 2 garbagevalue1 garbagevalue2”.
        //since 1 and 2 are values of previous block a, so they are copied in the new block b
        //and garbage values are printed in the new block of memory because till now no values are assigned in the new block of memory
    }


    for(int i = 0; i < n; i++)
    {
            printf(“%d ”,a[i]); //this will print values as 1 2 3...n
    }
//this will deallocate after the block of memory has been used , so that it can be reused.
free();
}

Example for calloc():

#include<stdio.h>
#include<conio.h>
#include<stdlib.h>

void main()
{
    int n;

    printf(“enter size of array”);
    scanf(“%d”, &n);

    int *a = (int)calloc(n*sizeOf(int)); //dynamically allocated array
    //if we do not initialize the values in the array then by default the calloc will assign zeros in the block of memory.
    //so if we comment the below for loop then it will print all values as zero on the console
    //and if we assign values by using the below for loop , then it print all the values that are assigned in the block of memory
    for(int i = 0; i < n; i++)
    {
        a[i]=i+1;//assigning values as 1,2,3...n;
    }

    for(int i = 0; i < n; i++)
    {
        printf(“%d ”,a[i]); //this will print values as 1 2 3...n
    }
}