在    int a[4][4]={
                 {2,5,1,8},
                 {7,1,6,4},
                 {0,2,5,4},
                 {3,0,2,1},
    };中，为什莫称if(i+j==3)
            s+=a[i][j];
为辅对角线元素和，不应该是if(i+j==4)
            s+=a[i][j];是辅对角线元素和吗?

谢谢