C语言编程题：定义一个5╳5的矩阵,求对角线上的元素之和.

#include
int main()
{
int a[5][5]={{1,2,3,4,5},{1,2,3,4,5},{1,2,3,4,5},{1,2,3,4,5},{1,2,3,4,5}};
int sum=0,i;
for (i=0;i