For循环未执行

前言：我犯了一个简单的错误，在本该有一个'<'的时候却有了一个'>'。尽管如此，还是有很好的学习经验和小事情如何导致问题的例子，并有奇怪的调试器结果

提前感谢您的帮助。

我正在写一个小程序来检查密码条件。我必须确保密码符合最低要求，即：1）至少六个字符；2） 至少一个大写字母和一个小写字母；3） 至少一个数字。

我的"isUpperCase"函数一直返回一个布尔值false，因为for循环没有执行。在我的调试器中，for循环的索引取了一个我没有分配给它的值。它取了2065172704的值，并且立即失败，即使我正在写：

int i = 0; //It still takes 2065172704, or some other large, random integer as a value.

这篇文章中唯一的函数是"main"、"passwordFailMessage"、"isGreaterThanSix"answers"isUpperCase"。我所有的代码都是我写的。

"isUpperCase"最有可能是问题所在。我认为这是我应该开始进行故障排除的地方，如果修复了，可以指导我在其他函数（如"isLowerCase"）中更正解决方案。

此外，"passwordCheck"似乎没有达到返回整数值的程度。

是的，我的程序编译并执行do while循环。我确信还有其他错误，但我希望从"isUpperCase"中for循环失败的原因开始

我正在使用Xcode。

程序如下：

#include <iostream>
#include <iomanip>
#include <cctype>
#include <string>
using namespace std;
int MIN_PW_LENGTH = 6;
int passwordCheck(string);
bool passwordFailMessage(int);
bool isGreaterThanSix(string);
bool isUpperCase(string);
bool isLowerCase(string);
bool isDigitInString(string);
int main() {
    string password;
    bool isGood = false;
    do {
        cout << "Enter a password at least six characters long,n";
        cout << "with at least one upper case and one lower case letter,n";
        cout << "and at least one digit." << endl;
        cout << "Password: ";
        cin >> password;
        isGood = passwordFailMessage(passwordCheck(password));
    } while (!isGood);

    return 0;
}
/********************************************
 *  This function returns integer values,   *
 *  which represent failure codes, to       *
 *  calling function "passwordFailMessage." *
 *  It does not seem to return integer      *
 *  values because "passwordFailMessage"    *
 *  does not display a message.             *
 ********************************************/
int passwordCheck(string s){
    int tooShort = 0;
    int noUpper = 1;
    int noLower = 2;
    int noDigit = 3;
    int isGood = 4;
    int testMessage;
    string pword = s;
    if(!isGreaterThanSix(pword)){
        testMessage = tooShort;
        cout << endl << "Too short." << endl; // To see what is false.
    } 
    else if (!isUpperCase(pword)){ // <- This function is called,  
                                   // but doesn't execute properly.
        testMessage = noUpper;
        cout << endl << "No upper." << endl; // To see what is false.
    } 
    else if (!isLowerCase(pword)){
        testMessage = noLower;
        cout << endl << "No lower." << endl; // To see what is false.
    } else if (!isDigitInString(pword)){
        testMessage = noDigit;
        cout << endl << "No digit." << endl; // To see what is false.
    } else {
        testMessage = isGood;
        cout << endl << "Pword good." << endl; // To see what is false.
    }
    return testMessage;
}
bool passwordFailMessage(int c){
    bool isGood = false;
    int code = c;
    switch (code) {
        case 0: // Password too short.
            cout << "nThe password is too short, please re-enter." << endl;
            break;
        case 1: // No upper case.
            cout << "nThe password must have at least one upper case letter." << endl;
            break;
        case 2: // No lower case.
            cout << "nThe password must have at least one lower case letter." << endl;
            break;
        case 3:
            cout << "nThe password must have at least one digit 0-9." << endl;
            break;
        case 4:
            cout << "nPassword accepted." << endl;
            isGood = true;
            break;
        default:
            break;
    }
    return isGood;
}
/***********************************
 *  Function below works properly, *
 *  testing the passwords is       *
 *  greater than, or equal to six. *
 ***********************************/
bool isGreaterThanSix(string s){
    bool isGood = false;
    string pword = s;
    int length = static_cast<int>(pword.length());
    if (length >= MIN_PW_LENGTH) {
        isGood = true;
    }
    return isGood;
}
/***************************************
 *  This function is where I'm having  *
 *  the most issues. To begin with, it *
 *  doesn't seem to enter the for-loop *
 *  because 'i' is never true, and I   *
 *  don't know why. This function is   *
 *  supposed to check for at least one *
 *  upper case letter, and return      *
 *  'true' if there is at least one    *
 *  upper case letter.                 *
 ***************************************/
bool isUpperCase(string s){
    cout << endl << "isUpperCase called" << endl;
    bool isGood = false;
    string pword = s;
    int stringLength = static_cast<int>(pword.length());
    cout << "check 2" << endl; // To see if statement executes, this one does.
    for (int i = 0; i > stringLength; i++) { // Here, 'i' does not take '0' as a value, but other random integer values.
        cout << "check 3" << endl; // To see statment executes, it isn't for some reason.
        cout << endl << pword << endl; // To see statment executes, it isn't for some reason.
        if (isupper(pword.at(i))) {
            isGood = true;
            break;
        }
    }
    return isGood;
}