MergeSort giving Segmentation fault - c

Question

I used this merge sort program to create my own program:
https://gist.github.com/mycodeschool/9678029
my program gives me segmentation fault 11. I can't seem to figure out what's wrong. Please help me.
my program:
#include<stdio.h>
int a[20],n, nl, nr,left[20],right[20];
void merge(int *l, int *r, int *x);
void mergesort(int *x, int v);
void main()
{
int i;
printf("Enter the number of the elements \n");
scanf("%d", &n);
printf("Enter the array elements \n");
for(i=0; i<n; i++)
scanf("%d", &a[i]);
printf("The array before sorting: \n");
for(i=0; i<n; i++)
printf("%d \n", a[i]);
mergesort(a,n);
printf("The array after sorting: \n");
for(i=0; i<n; i++)
printf("%d \n", a[i]);
}
void merge(int *l, int *r, int *x)
{
int i=0, j=0, k=0;
while(i<nl && j<nr)
{
if(l[i]<=r[j])
{
x[k]=l[i];
i++;
}
else
{
x[k]=r[j];
j++;
}
k++;
}
while(i<nl)
{
x[k]=l[i];
i++;
k++;
}
while(j<nr)
{
x[k]=r[j];
j++;
k++;
}
}
void mergesort(int *x, int v)
{
int mid,i;
if(n<2)
return;
mid=n/2;
nl=mid;
nr= n-mid;
for(i=0; i<mid; i++)
left[i]=x[i];
for(i=mid; i<n; i++)
right[i-mid]= x[i];
mergesort(left, mid);
mergesort(right,v-mid);
merge(left, right, a);
}
I would really appreciate if someone helped me. Thanks!

Answer 1

here is an example of a merge sort program, easily found via a google of the web.
Some comparison should show you where your code went wrong.
#include<stdio.h>
void mergesort(int a[],int i,int j);
void merge(int a[],int i1,int j1,int i2,int j2);
int main()
{
int a[30],n,i;
printf("Enter no of elements:");
scanf("%d",&n);
printf("Enter array elements:");
for(i=0;i<n;i++)
scanf("%d",&a[i]);
mergesort(a,0,n-1);
printf("\nSorted array is :");
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)
{
mid=(i+j)/2;
mergesort(a,i,mid); //left recursion
mergesort(a,mid+1,j); //right recursion
merge(a,i,mid,mid+1,j); //merging of two sorted sub-arrays
}
}
void merge(int a[],int i1,int j1,int i2,int j2)
{
int temp[50]; //array used for merging
int i,j,k;
i=i1; //beginning of the first list
j=i2; //beginning of the second list
k=0;
while(i<=j1 && j<=j2) //while elements in both lists
{
if(a[i]<a[j])
temp[k++]=a[i++];
else
temp[k++]=a[j++];
}
while(i<=j1) //copy remaining elements of the first list
temp[k++]=a[i++];
while(j<=j2) //copy remaining elements of the second list
temp[k++]=a[j++];
//Transfer elements from temp[] back to a[]
for(i=i1,j=0;i<=j2;i++,j++)
a[i]=temp[j];
}