我的程序中的无限循环

好的，所以对于我的学校项目，我们基本上是制作一个菜单，最多有 20 人输入信息并在需要时进行更改。一切都很好。但是，我们的作业让我们检查邮政编码的输入和整数值的帐户余额。我使用do-while循环进行邮政编码验证，直到输入正数和数字。但是，我得到了一个似乎无法修复的无限循环。这是我的代码。如果放入编译器，则错误位于第 57-68 行。每次我输入一个字母而不是一个整数时，我都会得到一个无限循环。但我不知道为什么。谢谢！

#include <iostream>
#include <iomanip>
#include <string>
#include <cstdlib>
using namespace std;
struct Account //Structure to be used throughout
{
     string CustomerName; 
     string CustomerAddress;
     string City;
     string State;
     int ZIPCode;
     string Telephone;
     int AccountBalance;
     string DateOfLastPayment;
};

//function prototypes 
void valueChangeFunc(string, Account[], int);//This function will be used in option 2 for editing a certain customer information

int main()
{
    Account array[20]; //Array to hold up to 20 customers 
    int choice;  //this will hold which option the user decides to make 1-4
    bool flagZip = false; //This will be used later on as a flag for a do-while loop
    bool flag = false; //This will be used as a flag for the do-while loop right now
    int index = 0; //Index for our customers. This tells how many customers have been entered
    do //This do while loop will continue to ask the user what option to do until array fills up with 20 people and 4 is not entered
    {
    cout << "1. Enter new account information n" <<endl 
     << "2. Change account information n" << endl
     << "3. Display all account informationn" <<endl
     << "4. Exit the program n" <<endl;
     cin >> choice; 
if (choice > 4 || choice <= 0)//If user enters a number bigger than 4 or less then or equal to 0. Error! 
cout << "Please enter a number between 1 and 4" << endl;
else if(choice == 1)
{
cout << "CustomerName: ";
        cin.ignore();
    getline(cin, array[index].CustomerName);
    cout << "CustomerAddress ";
    getline(cin, array[index].CustomerAddress);
    cout << "City: ";
    getline(cin, array[index].City);
    cout << "State: ";
    getline(cin, array[index].State);
    do
    {
    cout << "Zip Code: ";
    cin >> array[index].ZIPCode;
    cin.ignore();
    if (!isdigit(array[index].ZIPCode) && array[index].ZIPCode <= 0)
    cout << "Please enter a valid entry " << endl;
    else 
    flagZip = true;
    }while(flagZip == false);
    cout << "Telephone: ";
    getline(cin, array[index].Telephone);
    flagZip = false;
    do 
    {
    cout << "AccountBalance: ";
    cin >> array[index].AccountBalance;
    cin.ignore();
    if (array[index].AccountBalance <= 0)
    cout << "Please enter a valid entry " << endl;
    else
    flagZip = true;
    }while(flagZip == false); 
    cout << "DateOfLastPayment: ";
    getline(cin, array[index].DateOfLastPayment);

    cout << "nnCustomerName: " << array[index].CustomerName << endl;
    cout << "CustomerAddress " << array[index].CustomerAddress <<endl;
    cout << "City: " << array[index].City << endl;
    cout << "State: " << array[index].State << endl;
    cout << "Zip Code: " << array[index].ZIPCode << endl;
    cout << "Telephone: " << array[index].Telephone <<endl;
    cout << "AccountBalance: " << array[index].AccountBalance << endl;
    cout << "DateOfLastPayment: " << array[index].DateOfLastPayment << endl;
    cout << "You have entered information for customer number " << index << endl << endl;
    index++;
}
else if(choice == 2 && index != 0)
{
int num;
string valueChange;
do
{
cout << "  Customer number: ";
cin >> num;
if (num > (index-1) || num < 0)
cout << " There is no customer with that number " << endl;
}while (num > (index-1));
    cout << "nnCustomer Name: " << array[num].CustomerName << endl;
    cout << "Customer Address " << array[num].CustomerAddress <<endl;
    cout << "City: " << array[num].City << endl;
    cout << "State: " << array[num].State << endl;
    cout << "ZIPCode: " << array[num].ZIPCode << endl;
    cout << "Telephone: " << array[num].Telephone <<endl;
    cout << "Account Balance: " << array[num].AccountBalance << endl;
    cout << "Date of last payment: " << array[num].DateOfLastPayment << endl;
    cout << "You have requested information for customer number " << num << endl << endl;
    cout << "What value do you want to change? (press 4 to change 'Date of last payment') n"; 
    cin.ignore();
    getline(cin,valueChange);
    valueChangeFunc(valueChange, array, num);
    cout << "nHere is the new value you entered for " << valueChange << endl;
    cout << "nnCustomer Name: " << array[num].CustomerName << endl;
    cout << "Customer Address " << array[num].CustomerAddress <<endl;
    cout << "City: " << array[num].City << endl;
    cout << "State: " << array[num].State << endl;
    cout << "ZIPCode: " << array[num].ZIPCode << endl;
    cout << "Telephone: " << array[num].Telephone <<endl;
    cout << "Account Balance: " << array[num].AccountBalance << endl;
    cout << "Date of last payment: " << array[num].DateOfLastPayment << endl << endl;
}
else if(choice == 3 && index != 0)
{
    int num2;
do
{
    cout << "Enter the Customer Number to display information regarding that customer" << endl;
    cin >> num2; 
if (num2 > (index-1) || num2 < 0)
cout << "That Customer does not exist " <<endl; 
}
while(num2 > (index-1));

    cout << "nnCustomerName: " << array[num2].CustomerName << endl;
    cout << "CustomerAddress " << array[num2].CustomerAddress <<endl;
    cout << "City: " << array[num2].City << endl;
    cout << "State: " << array[num2].State << endl;
    cout << "Zip Code: " << array[num2].ZIPCode << endl;
    cout << "Telephone: " << array[num2].Telephone <<endl;
    cout << "AccountBalance: " << array[num2].AccountBalance << endl;
    cout << "DateOfLastPayment: " << array[num2].DateOfLastPayment << endl;
    cout << "You have entered information for customer number " << index << endl << endl;
}
else 
flag = true;
}while (flag == false);
    return 0;
}
void valueChangeFunc(string valueChange2, Account array[], int num)
{
    if (valueChange2 == "Customer Name" || valueChange2 == "Customer name" || valueChange2 == "customer Name" || valueChange2 == "customer name")
    {
    cout << "nEnter new value for Customer Name: " <<endl;
    getline(cin, array[num].CustomerName);
    }
    if (valueChange2 == "Customer Address" || valueChange2 == "Customer address" || valueChange2 == "customer Address" || valueChange2 == "customer address")
    {
    cout << "nEnter new value for Customer Address: " <<endl;
    getline(cin, array[num].CustomerAddress);
    }
    else if(valueChange2 == "city" || valueChange2 == "City")
    {
        cout << "nEnter new value for City: " << endl;
        getline(cin, array[num].City);
    }
    else if(valueChange2 == "state" || valueChange2 == "State")
    {
        cout << "Enter a value for State: " << endl;
        getline(cin,array[num].State);
    }
    else if(valueChange2 == "Zip Code" || valueChange2 == "zip Code" || valueChange2 == "Zip code" || valueChange2 == "zip code")
    {
        cout << "nEnter a value for Zip Code: " << endl;
        cin >> array[num].ZIPCode;
    } 
    else if(valueChange2 == "telephone" || valueChange2 == "Telephone")
    {
        cout << "nEnter a value for Telephone: " << endl;
        getline(cin, array[num].Telephone);
    }
    else if(valueChange2 == "Account Balance" || valueChange2 == "Account balance" || valueChange2 == "account Balance" || valueChange2 == "account balance")
    {
        cout << "nEnter a value for account balance: " << endl;
        cin >> array[num].AccountBalance;
    }
    else if(valueChange2 == "4")
    {
        cout << "nEnter the value for Date of last payment: " << endl;
        getline(cin, array[num].DateOfLastPayment);
    }
    else 
    cout << "Not entered correctly. Please enter a valid entry to edit " << endl;
}

再次一切正常，直到我开始使用循环来检查邮政编码的数字值。只有当我输入一个字母时，循环才会无限。它适用于负数和正数。