#include <stdio.h>

#include <stdlib.h>

#define  N  5

double fun ( int w[][N] )

{int i,j;

double m=0;

for (i=0;i<N;i++)

for (j=0;j<N;j++)

if (i==0||j==0||i==N-1||j==N-1)

m+=w[i][j];

m/=(4N-4);

return m;

}

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;void NONO ();

   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 );

   NONO( );

}

void NONO ()

{/* 本函数用于打开文件，输入数据，调用函数，输出数据，关闭文件。 */

  FILE *rf, *wf ;

  int i, j, a[5][5]; double s ;

  rf = fopen("in.dat","r") ;

  wf = fopen("out.dat","w") ;

  for(i = 0 ; i < 5 ; i++)

  for(j = 0 ; j < 5 ; j++) fscanf(rf, "%d ", &a[i][j]) ;

  s = fun(a) ;

  fprintf(wf, "%lf\n", s);

  fclose(rf) ;

  fclose(wf) ;

}