九度题目1391：顺时针打印矩阵

输入一个矩阵，按照从外向里以顺时针的顺序依次打印出每一个数字，例如，如果输入如下矩阵：
1 2 3 4
5 6 7 8
9 10 11 12
13 14 15 16
则依次打印出数字1,2,3,4,8,12,16,15,14,13,9,5,6,7,11,10.

#include <iostream>
#include<stdio.h>
using namespace std;

int main()
{
    int m,n,count;
    //cin>>m>>n;
    while(cin>>m>>n){     //多个测试样例，要用while循环，这里出错多次
    int a[m][n];
    count=m*n;
    for (int i=0; i<m; i++)
    {
        for (int j=0; j<n; j++)
        {
            cin>>a[i][j];
        }
    }

    int num=0,i=0,j=0;
     while (num<count)
     {
        while (j<n&&a[i][j]!=-1)
        {
            cout<<a[i][j]<<" ";
            a[i][j]=-1;
            j++;
            num++;
            //cout<<"j"<<j;
            //cout<<"A\n";
        }
        j--;
        i++;    //最终发现这里错了
        //cout<<"j"<<j;
        //cout<<"B\n";
        while(i<m&&a[i][j]!=-1)//短路所以后面不会越界
        {
            cout<<a[i][j]<<" ";
            a[i][j]=-1;
            i++;
            num++;
            //cout<<"C\n";
        }
        i--;
        j--;
        //cout<<"j"<<j;
        while (j>-1&&a[i][j]!=-1)
        {
            cout<<a[i][j]<<" ";
            a[i][j]=-1;
            j--;
            num++;
        }
        j++;
        i--;
        while (i>-1&&a[i][j]!=-1)
        {
            cout<<a[i][j]<<" ";
            a[i][j]=-1;
            i--;
            num++;
        }
        i++;
        j++;
     }
    printf("\n");
    }
    return 0;
}

注意事项

1.循环开始结束的重要节点，边界条件

2. 九度垃圾，多个测试样例要用while输入，单个一直报错还不告诉错在哪里，莫名其妙