C program to add value in Spiral matrix Format

C program to add value in Spiral matrix Format

#include < stdio.h >
#include < conio.h > 

void main()
{
 int m[20][20],i,j;
 int p,q,r,hr,r,c,cnt; 
 clrscr();
 printf("\nEnter r & c :");
 scanf("%d %d",&r,&c);
 cnt = 1;
 r = 0; p = 0;
 hr = r - 1;
 q = c - 1;
 while ( r <=hr && p <= q )
 {
  i = r;
  for(j=p;j <= q;j++)
  {
   m[i][j] = cnt++; 
   j = q;
   for(i=r+1;i<=hr;i++)
   {
    m[i][j] = cnt++; 
    if( r != hr )
    {
     i = hr;
     for(j=q-1;j>=p;j--)
     m[i][j] = cnt++;
    } 
    if ( p != q )
    {
     j = p;
     for(i=hr-1;i>r;i--)
     m[i][j] = cnt++;
    }
   }
  }
  r++;p++;
  hr--;q--;
 } 
 printf("\nSpirally filled matrix is\n");
 for(i=0;i < r;i++)
 {
  for(j=0;j<c;j++)
  {
   printf("%4d",m[i][j]);
   printf("\n");
  }  
 }