Merge Sort Program In C

Here I am providing you with Merge Sort program in c.
```#include<stdio.h>

void mergesort(int a[],int i, int j);
void merge(int a[],int p , int q, int r1);

int main()
{
int a[20],i,n,item;
printf("Enter number of elements in array : ");
scanf("%d",&n);

// Inputting elements
for(i=0;i<n;i++)
{
printf("Enter number %d: ",i+1);
scanf("%d",&a[i]);
}

// Displaying Elements before merge sort
printf("Items in the array are : ");
for(i=0;i<n;i++)
{
printf("%d ",a[i]);
}

//Applying merge sort
mergesort(a,0,n-1);

// Displaying elements after merge sort
printf("\nElements after merge sort : ");
for(i=0;i<n;i++)
{
printf("%d ",a[i]);
}
return 0;
}

void mergesort(int a[],int i, int j)
{
int mid;
if(i>=j)
return;

else
{
mid=(i+j)/2;
mergesort(a,i,mid);
mergesort(a,mid+1,j);
merge(a,i,mid,j);
}
}

void merge(int a[],int p , int q, int r)
{
int n1=q-p+1;
int n2=r-q;
int left[n1+1];
int right[n2+1];

int i=0;
int j=0;
int k=0;

for(i=0;i<n1;i++)
{
left[i]=a[p+i];
}

for(i=0;i<n2;i++)
{
right[i]=a[q+i+1];
}

left[n1]=9999;
right[n2]=9999;

i=0;
j=0;

for(k=p;k<=r;k++)
{

if(left[i]<right[j])
{
a[k]=left[i];
i++;
}

else
{
a[k]=right[j];
j++;
}
} ```
```}

```