Implementation of Quicksort in C language

qsort.c

// Implementation of Quicksort in C language
#include<stdio.h>
int i,j,n,pivot,a[20];
void quick(int *a, int left, int right);
void swap(int *a, int i, int j);
void main()
{
   int a[20];
   printf("Enter the limits: ");
   scanf("%d",&n);
   printf("Enter the elements: ");
   for(i=0;i<n;i++)
      scanf("%d",&a[i]);
   quick(a,0,n-1);
   printf("The sorted list is ... \n");
   for(i=0;i<n;i++)
      printf("%d\n",a[i]);
}
void quick(int *a, int first, int last)
{
   if(first<last)
   {
      pivot=a[first];
      i=first;
      j=last;
      while(i<j)
      {
         while(a[i]<=pivot && i<last)
            i++;
         while(a[j]>=pivot && j>first)
            j--;
         if(i<j)
            swap(a,i,j);
      }
      swap(a,first,j);
      quick(a,first,j-1);
      quick(a,j+1,last);
   }
}
void swap(int *a, int i, int j)
{
   int temp;
   temp=a[i];
   a[i]=a[j];
   a[j]=temp;
}