Question

I’m doing a problem where it asks to input an account number, which consists only of four digits. This has to be accomplished with basic beginner C++.

I need to figure out a way to restrict the input of the integer to four digits. A user should be able to put in 0043 or 9023 or 0001 and it should be an acceptable value….

I think I know how to accomplish it with a string…. getline(cin,input) and then check if input.length()==4?

But I’ve no idea how I would even do this with an integer input.

Answer 1

Something like this should work. Once the user enters something with exactly four characters you can validate it. The rest of the logic is up to you.

#include <iostream>
#include <string>

int main() {
    std::cout << "Enter a PIN Number: ";
    std::string pinStr;
    while(std::getline(std::cin,pinStr) && pinStr.size() != 4) {
        std::cout << "Please enter a valid value\n";
    }
}

Should you want to store it in an integer form, holding the integers in an std::vector might be beneficial. You can do this easily (loop unrolling was for clarity):

#include <iostream>
#include <string>
#include <vector>

int main() {
    std::cout << "Enter a PIN Number: ";
    std::string pinStr;
    while(std::getline(std::cin,pinStr) && pinStr.size() != 4 ) {
        std::cout << "Please enter a valid value\n";
    }
    std::vector<int> pin;
    pin[0] = pinStr[0] - '0';
    pin[1] = pinStr[1] - '0';
    pin[2] = pinStr[2] - '0';
    pin[3] = pinStr[3] - '0';

    //pin now holds the integer value.
    for(auto& i : pin)
        std::cout << i << ' ';
}

You can see it running here