C++无法读入的问题

Question

这是我的代码，我一编译运行就连输入都没法输入，这是为啥？

#include <iostream>

using namespace std;

int main(){
    
    int n;
    int b[n][2];
    int a[n][n],cx,cy,mid;
    while (true){
        cin>>n;
        if (n==0) break;
        for (int i=0;i<=n/2;i++){
        for (int j=0;j<2;j++){
            b[i][j]=i*(j+1);
        }
    }
        if (n%2==0){
            cx=n/2-1,cy=n/2-1;
             mid=n/2;
        }
        else{
            cx=n/2,cy/2;
             mid=(n+1)/2;
        }

        for (int i=0;i<=n/2;i++){
            for(int j=0;j<=n/2;j++){
                int d=abs(i-cx)+abs(j-cy);
                for (int k=0;k<=n/2;k++){
                    if (d>=b[k][0]&&d<=b[k][1]){
                        a[i][j]=mid-k;
                        a[i][n-1-j]=a[i][j];
                        a[n-1-i][j]=a[i][j];
                    }
                }
                
        }
    }
    for (int i=0;i<n;i++){
        for (int j=0;j<n;j++){
            cout<<a[i][j]<<" ";
        }
    cout<<endl;
}
    
    }
    
    
    
    
    
    return 0;}
    

Answer 1

添加初始值即可，否则随机选取的值是不可预料的，while循环也进不了！可以尝试打印一下未初始化的n值。

#include <iostream>

using namespace std;

int main()
{

    int n=0; // 添加初始值
    int b[n][2];
    int a[n][n], cx, cy, mid;

    
    while (true)
    {
       // cout<<"here"<<endl;
        cin >> n;
        if (n == 0)
            break;
        for (int i = 0; i <= n / 2; i++)
        {
            for (int j = 0; j < 2; j++)
            {
                b[i][j] = i * (j + 1);
            }
        }
        if (n % 2 == 0)
        {
            cx = n / 2 - 1, cy = n / 2 - 1;
            mid = n / 2;
        }
        else
        {
            cx = n / 2, cy / 2;
            mid = (n + 1) / 2;
        }

        for (int i = 0; i <= n / 2; i++)
        {
            for (int j = 0; j <= n / 2; j++)
            {
                int d = abs(i - cx) + abs(j - cy);
                for (int k = 0; k <= n / 2; k++)
                {
                    if (d >= b[k][0] && d <= b[k][1])
                    {
                        a[i][j] = mid - k;
                        a[i][n - 1 - j] = a[i][j];
                        a[n - 1 - i][j] = a[i][j];
                    }
                }
            }
        }
        for (int i = 0; i < n; i++)
        {
            for (int j = 0; j < n; j++)
            {
                cout << a[i][j] << " ";
            }
            cout << endl;
        }
    }

   return 0;

}