我无法让我的密码验证程序正常工作。我的循环似乎只迭代一次，我只是将“它”作为输出来查看它是否在不断迭代，但事实并非如此。我不确定为什么，布尔值正在工作，但它只迭代一次，如果我的第一个字母是小写，那么它会说我需要一个大写和一个数字，反之亦然，如果我的第一个字符是数字或大写。这是一个家庭作业，但我有点迷茫。任何帮助将不胜感激。
#include<iostream>
#include<string>
#include<cctype>
using namespace std;
int main()
{
const int LENGTH = 20;
char pass[LENGTH];
cout << "Enter a password, that's at least 6 characters long, one uppercase, one lowercase letter ";
cout << " and one digit." << endl;
cin.getline(pass,LENGTH);
bool isdig = true;
bool isdown = true;
bool isup = true;
bool correct = false;
for(int index = 0; correct == false; index++)
{
cout << "it" << endl;
if(isupper(pass[index]) == 0)
{isup = false;}
if(islower(pass[index]) == 0)
{isdown = false;}
if(isdigit(pass[index]) == 0)
{isdig = false;}
if(isdig == true && isup == true && isdown == true)
{correct = true;}
if(index = LENGTH - 1)
{
if(isdig == false)
{cout << "Your password needs a digit." << endl;}
if(isup == false)
{cout << "Your password needs an uppercase letter." << endl;}
if(isdown == false)
{cout << "Your password needs a lowercase letter." << endl;}
cout << "Re-enter another password. " << endl;
cin.getline(pass,LENGTH);
index = 0;
isdown = true;
isup = true;
isdig = true;
}
}
system("pause");
return 0;
}