题目:

//while循环实现

int main()
{
    int n;
    cout << "请输入边长：";
    cin >> n;
    int i = 1; 
    while (i <= n)
    { // 控制行数
        int j = 1;
        while (j <= n)
        { // 控制列数
            if (i == 1 || i == n || j == 1 || j == n)
            {
                cout << "*";
            }
            else
            {
                cout << " ";
            }
            j++;
        }

        cout << endl;
        i++;
    }

    return 0;
}

//for循环实现（更简单）

#include <iostream>
using namespace std;

int main()
{
    int n;

    cout << "请输入边长：";
    cin >> n;
    for(int i=1;i<=n;i++){
    	for(int j=1;j<=n;j++){
    		if (i == 1 || i == n || j == 1 || j == n)
            {
                cout << "*";
            }
            else
            {
                cout << " ";
            }
		}
		cout<<endl;
	}
    return 0;
}