求出数组周边元素的平均值并作为函数值返回给主函数中的s

#include <stdio.h>
#include <stdlib.h>
#define  N  5
double fun ( int w[][N] )
{
    int i,j,n=0;
    double s=0,av;
    for(i=0;i<N;i++)
    {
        s+=w[i][0];
        n++;
        s+=w[i][N-1];
        n++;
    }
    for(j=1;j<N-1;j++)
    {
        s+=w[0][j];
        n++;
        s+=w[N-1][j];
        n++;
    }
    av=s/n;
    
    return av; 
}

main ( )
{  int a[N][N]={0,1,2,7,9,1,9,7,4,5,2,3,8,3,1,4,5,6,8,2,5,9,1,4,1};
   int i, j;
   double s ;
   printf("***** The array *****\n");
   for ( i =0;  i<N; i++ )
   {  for ( j =0; j<N; j++ )
     {  printf( "%4d", a[i][j] ); }
        printf("\n");
   }
   s = fun ( a );
   printf ("***** THE  RESULT *****\n");
   printf( "The sum is :  %lf\n",s );
}