填空完善程序，用行指针实现求一个二维数组四周元素的平均值。源程序保存为tk12_1.c。

Question

#include "stdio.h"
#define M 4
#define N 5
float fun(int (*p)[N],int m)
{ int i,j,k=0;
float sum,ave;
sum=0;
for(i=0;i<m;i++)
for(j=0;j<N;j++)
if /************found************/
(i==0||i==_________||j==0||j==____________)
{ sum+=p[i][j];
k++;

}
ave=sum/k;
return ave;

}
main()
{ int a[M][N]={{1,2,3,4,5},{6,7,8,9,10},{11,12,13,14,15},{16,17,18,19,20}};
int i,j;
float ave;
for(i=0; i<M;i++)
{ for(j=0;j<N;j++)
printf("%4d",a[i][j]);
printf("\n");
}
/************found************/
ave=___________________;
printf("average=%.2f\n",ave);
system("pause");
}

Answer 1

(i==0||i==_________||j==0||j==____________)
->
(i==0||i==m-1||j==0||j==N-1)

ave=___________________;
->
ave=fun(a, M);