Program for Merge Sort is given below:

//Merge sort Program

#include<stdio.h>
void merge(int A[],int lb,int mid,int ub)
{
    int i,j,k,B[50];
    i=lb;
    j=mid+1;
    k=lb;
    while(i<=mid && j<=ub)
    {
        if(A[i]<=A[j])
        {
            B[k] = A[i];
            i++;
            k++;
        }
        else
        {
            B[k]=A[j];
            j++;
            k++;
        }
    }
    if(i>mid)
    {
        while(j<=ub)
        {
            B[k]=A[j];
            j++;
            k++;
        }
    }
    else
    {
        while(i<=mid)
        {
            B[k]=A[i];
            i++;
            k++;
        }
    }
    for(k=lb;k<=ub;k++)
    {
        A[k]=B[k];
    }
}
void mergesort(int A[],int lb,int ub)
{
    if(lb<ub)
    {
        int mid=(lb+ub)/2;
        mergesort(A,lb,mid);
        mergesort(A,mid+1,ub);
        merge(A,lb,mid,ub);
    }
}
void printArray(int array[], int size)
{
    for (int i = 0; i < size; ++i)
    {
        printf("%d  ", array[i]);
    }
    printf("\n");
}
int main()
{
    int n,A[50];
    printf("Enter the size of the array :");
    scanf(" %d",&n);
    printf("Enter the array :\n");
    for(int i=0;i<n;i++)
    {
        scanf(" %d",&A[i]);
    }
    printf("the unsorted array is :\n");
    printArray(A,n);
    mergesort(A,0,n-1);
    printf("the sorted array is :\n");
    printArray(A,n);
    return 0;
}

Output

Enter the size of the array :9
Enter the array :
15 5 24 8 1 3 16 10 20
the unsorted array is :
15  5  24  8  1  3  16  10  20
the sorted array is :
1  3  5  8  10  15  16  20  24