程序代码：

root@~ #cat duijiao.c
#include <stdio.h>

int main (void) {

        int sa=0,sb=0,i,j;
        int a[4][4];
        for(i=0;i<4;i++) {
                for(j=0;j<4;j++) {
                        scanf("%i",&a[i][j]);
                }
        }
//
        for(i=0,j=0;i<4;i++,j++)
                sa+=a[i][j];

//
        for(i=0,j=3;i<4;i++,j--)
                sb+=a[i][j];

        printf("Left diagonal sum=%i Right diagonal sum=%i\n",sa,sb);

        return 0;

}

root@~ #./duijiao
1 2 3 4
1 2 3 4
1 2 3 4
9 9 9 9
Left diagonal sum=15 Right diagonal sum=18
root@~ #./duijiao
1 2 3 4
5 6 7 8
1 2 3 4
5 6 7 8
Left diagonal sum=18 Right diagonal sum=18
root@~ #

程序代码：

#include <stdio.h>

int main (void) {
    int s = 0, i;
    int a[4][4] = {0}, * p;
    for (p = &a[0][0], i = 0; i < 16; p++, i++) {
        scanf("%d", p);
    }
    for (p = &a[0][0], i = 0; i < 4; , p += 5, i++) {
        s += *p;
    }
    printf("The sum of elements on diagonal top-left to bottom-right is: %d", s);
    for (p = &a[0][3], i = 0; i < 4; , p += 3, i++) {
        s += *p;
    }
    printf("The sum of elements on diagonal top-right to bottom-left is: %d", s);
    return 0;
}