Merge Sort is a sorting technique which divides the array into sub-arrays which have size 2 and merge (combined) adjacent (near) pair. After first process you have n/2 array of size 2. this process is repeated until there is only one array remaining of size n. http://www.tutorial4us.com/data-structure/c-merge-sort

1. /*** program of merge sort ****
* http://www.tutorial4us.com/data-structure/c-merge-sort */
#include<stdio.h>
#include<conio.h>
void mergesort(int a[],int n)
{
int b[50],c,low1,high1,high2,low2;
int i,k,j;
c=1;
while(c<n)
{
low1=0;
k=0;
while(low1+c<n)
{
low2=low1+c ;
high1=low2-1;
if(low2+c-1<n)
high2=low2+c-1;
else
high2=n-1;
i=low1;

2. j=low2;
while(i<=high1 && j<=high2)
{
if(a[i]<=a[j])
b[k++]=a[i++];
else
b[k++]=a[j++];
}
while(i<=high1)
b[k++]=a[i++];
while(j<=high2)
b[k++]=a[j++];
low1=high2+1;
}
i=low1;
while(k<n)
b[k++]=a[i++];
for(i=0; i<n; i++)
a[i]=b[i];
c=c*2;
}
}
main()

3. {
int a[20],i,n;
clrscr();
printf("How many elements you want to enter: ");
scanf("%d",&n);
printf("Enter any %d elements: n",n);
for(i=0; i<n; i++)
{
scanf("%d",&a[i]);
}
printf("nnList Befor Sorting : ");
for(i=0; i<n; i++)
{
delay(400);
printf("%5d",a[i]);
}
mergesort(a,n);
printf("nnList After Sorting : ");
for(i=0; i<n; i++)
{
delay(400);
printf("%5d",a[i]);

4. }
getch();
return 0;
}