银行记录 我想要求用户输入一个 4 位数的密码而不是字母

Question

I want my program to ask the user to input a 4 pin code (only numbers) and that it will accept no letters. It does accept no letters but each time I enter a pin the program doesn't care about the 4 numbers that I ask, you can input 1 number , so as, 10 numbers and it will still work. I want it to absolutely input a 4 pin code I tried many solution, such as, the if(pin>999 && pin<=9999) technique and it doesn't work... there is my code so far for that part. Many thanks in advance for the help of those who can explain me my wrongs

#include <iostream>
#include <string>
#include <algorithm>
#include <cmath>

using namespace std;

bool clientnumberlength(string pin) {

    bool status = true;
    if (pin.length() != 4) {
        status = false;
    }
    return status;
}


int main() {



    int clientnumber = 4;


    cout << "Welcome to my bank incorporation" << endl;
    cout << "Please enter your 4 pin customer number" << endl;

    while (!(cin >> clientnumber)) {
        string PIN;
        cin >> PIN;

        if (clientnumberlength(PIN) == 4) {
            cout << "PIN accepted" << endl;
            cin.clear();
            cin.ignore(numeric_limits<streamsize>::max(), '\n');

        }
        else {
            cout << "PIN refuser" << endl;
            cout << "Please enter your 4 pin customer number" << endl;
            cin.clear();
            cin.ignore(numeric_limits<streamsize>::max(), '\n');
        }
    } 


    return 0;
}

Answer 1

You can't really put restrictions on what is inputted through std::cin . You can either hope the user will input numbers, or look into making a more structured app with events and everything, which would be more time consuming. You can also have the user input a string, remove any non-numerical characters, check if the length is 4 and eventually ask to input another one if the conditions are not met.