Thinking:
(1)Defines a two-dimensional array a[3][3];
(2)Input;
(3)Calculate a[1][1],a[2][2],a[3][3];
(40Output.
// date:2020/3/3
// author:xiezhg5
#include <stdio.h>
int main(void)
{
int a[3][3],sum=0; //定义一个3 ×3的矩阵,sum初始化
int i,j; //i用来计行数,j用来计列数
printf("请输入数据:\n");
//for循环控制输入
for(i=0;i<3;i++)
for(j=0;j<3;j++)
scanf("%d",&a[i][j]);
//计算对角线元素和 //a[11],a[22],a[33]
for(i=0;i<3;i++)
sum=sum+a[i][j];
printf("sum=%d\n",sum);
return 0;
}