最初代码删掉了-----------------修改后的:#include <stdio.h>#define N 20int main(){int n,i,j;int sum=0;//定义二位数组int a[N][N];printf("n=?");scanf("%d",&n);for(i=0;i<n;i++){for(j=0;j<n;j++){a[i][j]=rand()%20;if(i==j)//计算主对角线之和sum+=a[i][i];}}//输出数组printf("矩阵:\n");for(i=0;i<=n;i++){for (j=0;j<=n;j++){printf("%5d",a[i][j]);}printf("\n");}printf("Sum=%d\n",sum);return 0;}