#include <stdio.h>
int main()
{
??? int arr[3][3] = {{1,2,3},{4,5,6},{7,8,9}};
??? int i,j;
??? int sum=0;
??? for(i=0;i<3;i++)
??? {
?????? for(j = 0; j < 3; j++)
?????? {
?????????? if(i % 2 == 0 && j % 2 == 0)
?????????? {
?????????????? sum += arr[i][j];
?????????? }
?????? }
??? }
??? sum += arr[1][1];
??? printf("對角線元素之和是：%d\n",sum);
??? return 0;???
}

1%2 !=0? if語句中不能判斷么， 為什么最后還要加一個sum += arr[1][1];