Credit Card Validator using C++ (With Source Code)

Credit Card Validator using C++ (With Source Code)

Hello, coders. Welcome to the codewithrandom blog. In this article, we will learn how to create a Credit Card Validator using C++ (With Source Code).

A credit card validator is an application or a software which verifies the authenticity and validity of credit card numbers. This software uses a mathematical algorithm, known as the Luhn algorithm, to determine whether a credit card number is valid or not.

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A credit card validator can be used for a number of purposes, including fraud prevention, chargeback reduction, and proper billing. Credit card validators are used by merchants and financial institutions to protect themselves against fraudulent transactions and to verify that they only accept authentic credit card payments. We will be creating a credit card validator using C++ programming language.

How does the Luhn Algorithm works?

The Luhn algorithm works by checking the sum of the digits of a credit card number against a predefined formula. If the sum of the digits meets the formula requirements, then the number is considered valid. However, if the sum of the digits does not meet the formula requirements, then the number is considered invalid.

Overview of the UI:

• This program uses the Luhn Algorithm to validate a CC number.
• You can enter ‘exit’ anytime to quit.
• Please enter a CC number to validate:

The user will enter a Credit card number. If according to the Luhn algoithm, the CC number is valid, then the program will display ‘valid’ else ‘invalid’.

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Credit Card Validator using C++ Source code:

You can directly use this code by copying it in your IDE to understand the working and then can create it by understanding the project.

#include <stdio.h>
#include <iostream>
#include <string>

using namespace std;

bool isNumberString(const string& s) {
    int len = s.length();
    for (int i = 0; i < len; i++) {
        if (s[i] < '0' || s[i] > '9')
            return false;
    }
    return true;
}

int main() {
    string ccNumber;
    
    cout << "This program uses the Luhn Algorigthm to validate a CC number." << endl;
    cout << "You can enter 'exit' anytime to quit." << endl;
    
    while (true) {
        
        cout << "Please enter a CC number to validate: ";
        cin >> ccNumber;
        
        if (ccNumber == "exit")
            break;
        
        else if (!isNumberString(ccNumber)) {
            cout << "Bad input! ";
            continue;
        }
            
        int len = ccNumber.length();
        int doubleEvenSum = 0;
        
        // Step 1 is to double every second digit, starting from the right. If it
        // results in a two digit number, add both the digits to obtain a single
        // digit number. Finally, sum all the answers to obtain 'doubleEvenSum'.   
        
        for (int i = len - 2; i >= 0; i = i - 2) {
            int dbl = ((ccNumber[i] - 48) * 2);
            if (dbl > 9) {
                dbl = (dbl / 10) + (dbl % 10);
            }
            doubleEvenSum += dbl;
        }
        
        // Step 2 is to add every odd placed digit from the right to the value
        // 'doubleEvenSum'.
        
        for (int i = len - 1; i >= 0; i = i - 2) {
            doubleEvenSum += (ccNumber[i] - 48);
        }
        
        // Step 3 is to check if the final 'doubleEvenSum' is a multiple of 10.
        // If yes, it is a valid CC number. Otherwise, not.
        
        cout << (doubleEvenSum % 10 == 0 ? "Valid!" : "Invalid!") << endl;
        
        continue;        
    }

    return 0;
}

Now let us understand the code:-

• After writing the header of the code with the required libraries such as stdio.h, iostream and string.
• We will define a function called “isNumberString” of type boolean which will take a string as a parameter and then checks if it contains only numeric characters. It uses a for loop and an if control statement.
• The main() function will display a message using cout. It displays that the program uses the Luhn Algorithm to validate a CC number and you can enter ‘exit’ anytime to quit.
• We will create a while loop with true condition. The loop will ask the user to enter the CC number to validate the credit card. The program will read the user’s input from the cin – standard input stream and then store it in a string variable called ccNumber. If the user types “exit”, the loop breaks and the program terminates.

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The Luhn Algorithm works as follows:

• Step 1 is to double every second digit, starting from the right. If it results in a two digit number, add both the digits to obtain a single digit number. Finally, sum all the answers to obtain ‘doubleEvenSum’.

  For this step we will create a for loop and implement the Luhn algorithm by looping over the credit card number’s digits, starting from the rightmost digit. The loop doubles every second digit and adds the result to a variable called ‘doubleEvenSum’.
   
• Step 2 is to add every odd placed digit from the right to the value ‘doubleEvenSum’.

  We will create another for loop. This loop will add all the odd-placed digits to ‘doubleEvenSum’. It will check if ‘doubleEvenSum’ is a multiple of 10 and outputs the result (either “Valid!” or “Invalid!”).

  This sums up our project of Credit Card Validator using C++.
   

Final Output of credit card validator using C++:-

Here is an example to show how this project works 

Conclusion

Overall, this program implements the Luhn Algorithm for credit card validation, including input/output management and error checks. We have reached the end of this article and have a lot more projects in C++ coming so stay tuned. We have started with awesome and fun projects for you all to understand C++. Learning C++ by creating fun projects makes learning easy and interesting.

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FAQ on Credit Card Validator