C语言_求一个3*3矩阵对角线元素之和

main()
{
float a[3][3],sum=0;
int i,j;
printf("please input rectangle element:\n");
for(i=0;i<3;i++)
for(j=0;j<3;j++)
scanf("%f",&a[i][j]);
sum=a[0][0]+a[0][2]+a[1][1]+a[2][0]+a[2][2];
printf("duijiaoxian he is %6.2f",sum);
}

main()
{
float a[9],sum=0;
int i,j;
printf("please input rectangle element:\n");
for(i=0;i<9;i++)
scanf("%f",&a[i]);
for(int j=0;j<9;j++)
if(j%2==0)
sum+=a[j];
printf("duijiaoxian he is %6.2f",sum);
}