C program to sort an array using merge sort

#include <stdio.h>
#define N 100
void mergesort(int [],int,int);
void merge(int [],int,int,int);
main()
{
int i,n;
int a[N];
printf("Enter the size of the array\n");
scanf("%d",&n);
printf("Enter the numbers...\n");
for(i=1;i<=n;i++)
scanf("%d",&a[i]);
mergesort(a,1,n);
printf("Sorted array is....\n");
for(i=1;i<=n;i++)
printf("%2d\n",a[i]);
}
void mergesort(int a[],int l,int u)
{
int m;
if(l<u)
{
m=(l+u)/2;
mergesort(a,l,m);
mergesort(a,m+1,u);
merge(a,l,m,u);
}
}
void merge(int a[],int l,int m,int u)
{
int n1,n2,i,j,k;
n1=(m-l)+1;
n2=u-m;
int L[n1],R[n2];
for(i=1;i<=n1;i++)
{
L[i]=a[i+l-1];
}
for(j=1;j<=n2;j++)
{
R[j]=a[m+j];
}
L[n1+1]=9999;
R[n2+1]=9999;
i=1;
j=1;
for(k=l;k<=u;k++)
{
if(L[i]<R[j])
{
a[k]=L[i];
i++;
}
else
{
a[k]=R[j];
j++;
}
}
}