6-7 average the surrounding elements of a two-dimensional array

This topic requires the average value of the surrounding elements of a two-dimensional array .

Function interface definition ：

double avg(int a[][N]);

The function value returns the average value of the surrounding elements .

Sample referee test procedure ：

#include <stdio.h>
#define M 3
#define N 4

double avg(int a[][N]);

int main()
{
    int i,j,a[M][N];
    double av;
    for(i=0;i<M;i++)
        for(j=0;j<N;j++)
            scanf("%d",&a[i][j]);
    av=avg(a);
    printf("%f",av);
    return 0;
}

/*  Please fill in the answer here  */

sample input ：

1 2 3 4
5 6 7 8
9 1 2 3

sample output ：

Here is the corresponding output . for example ：

3.800000

Ideas ： This problem requires us to find the average value of the surrounding elements of a two-dimensional array , Just traverse the surrounding elements and get the average value , Relatively simple , The code is as follows ：

double avg(int a[][N])
{
    int i, j,k=0;//i j  Is a cyclic variable  k It is used to calculate the sum of several numbers , Easy to calculate the average value 
    double sum=0;// Sum up 
    double av;// Average. 
    for (i = 0; i < M; i++)// Outer loop control line , Inner loop control column 
    {
        for (j = 0; j < N; j++)
        {
            if (i == 0 || j == 0 || i == (M-1) || j == (N-1))// As long as it is the first or last line . First of all                             
                                                            // The number of columns and the last column are peripheral numbers .
            {
                k++;
                sum += a[i][j];
            }
        }
    }
    av = sum/ k;
    return av;
}