真题编程题5：求出二维数组周边元素之和，作为函数值返回，二维数组中的值在主函数中赋予。

#include
#include
#include
#define  M  4
#define  N  5
int fun(int a[M][N])//考试内容 编写函数fun
{
	int i, j;//定义循环所用变量i,j 
	int sum=0; //定义求和总数 
	for (i = 0; i < M; i++)//双层循环遍历整个数组i代表行，j代表列 
		for (j = 0; j < N; j++)
		{
			if (i == 0 || i == M - 1 || j == 0 || j == N - 1) //判断最外层元素
			{
				sum += a[i][j];	 //求和
			}
		}
	return sum;  //返回给主函数
}
void main()
{
	int aa[M][N] = { {1,3,5,7,9},{2,9,9,9,4},{6,9,9,9,8},{1,3,5,7,0} };
	int i, j, y;
	system("CLS");
	printf("The original data is :\n ");
	for (i = 0; i < M; i++)
	{
		for (j = 0; j < N; j++)
			printf("%6d ", aa[i][j]);
		printf("\n ");
	}
	y = fun(aa);
	printf("\nThe sun: %d\n ", y);
	printf("\n ");
}