Password detection (C ++ programming third edition 5.27)

Password rules are as follows:
1. The password must have at least eight characters.
2. The password must contain only letters and numbers.
3. The password must contain at least two numbers.

head.h

#include <iostream>
#include <string>
#include <cctype>


using namespace std;

void judge(string& s);

DetectPassword.cpp

#include "head.h"

void judge(string& s)
{
	int q; //返回密码长度
	int r = 0; //返回数字个数
	q = s.size();
	if (q < 8)
	{
		cout << "密码位数小于八位，请重新输入" << endl;
		return ;
	}
	else 
   {
		for (int i = 0;i < s.size();i++)
		{
		
			if (isdigit(s.at(i)) || isalpha(s.at(i)))//isdigit用来判断字符是否为数字
			{
				if(isdigit(s.at(i)))
					r++;
			}
			else
			{
				cout << "输入非法字符请重新输入" << endl;
				return ;
			}
		}

		if (r < 2) {
			cout << "数字元素个数小于二请重新输入" << endl;
			return;
		}
		else
		{
			cout << "valid password" << endl;
			return ;
		}

	}
}
int main()
{
	string s;
	cout << "请输入密码" << endl;
	cout << "Password:";
	cin >> s;
    judge(s);
	return 0;
}