warning：输出图案时注意字符数

#include <iostream>
using namespace std;
int main()
{
    int a;
    while (cin >> a)
    {
        int i, j;
        for (i = 0; i < a; ++i)
        {
            for (j = 0; j < a; ++j)
            {
                if (i == 0 || i == a - 1)
                    cout << "* ";
                else if (j == 0 || j == a-1 )
                    cout << "* ";
                else cout << "  ";//两个空格
            }
            cout << endl;
        }
    }
}