How to validate CVV number using Regular Expression

Given string str, the task is to check whether it is a valid CVV (Card Verification Value) number or not by using Regular Expression. 
The valid CVV (Card Verification Value) number must satisfy the following conditions: 

1. It should have 3 or 4 digits.
2. It should have a digit between 0-9.
3. It should not have any alphabet or special characters.

Examples: 

Input: str = "561" 
Output: true 
Explanation: 
The given string satisfies all the above mentioned conditions. Therefore, it is a valid CVV (Card Verification Value) number.

Input: str = "50614" 
Output: false 
Explanation: 
The given string has five-digit. Therefore, it is not a valid CVV (Card Verification Value) number.

Input: str = "5a#1" 
Output: false 
Explanation: The given string has alphabets and special characters. Therefore, it is not a valid CVV (Card Verification Value) number. 

Approach: The idea is to use Regular Expression to solve this problem. The following steps can be followed to compute the answer. 

• Get the String.
• Create a regular expression to check the valid CVV (Card Verification Value) number as mentioned below:

regex = "^[0-9]{3, 4}$";

• Where: 
  
  • ^ represents the starting of the string.
  • [0-9] represents the digit between 0-9.
  • {3, 4} represents the string that has 3 or 4 digits.
  • $ represents the ending of the string.
• Match the given string with the regular expression. In Java, this can be done by using Pattern.matcher().
• Return true if the string matches with the given regular expression, else return false.

Below is the implementation of the above approach:

// C++ program to validate the
// CVV (Card Verification Value) number
// using Regular Expression
#include <iostream>
#include <regex>
using namespace std;

// Function to validate the CVV 
// (Card Verification Value) number
bool isValidCVVNumber(string str)
{

    // Regex to check valid CVV 
    // (Card Verification Value) number
    const regex pattern("^[0-9]{3,4}$");

    // If the CVV (Card Verification Value)
    //  number is empty return false
    if (str.empty()) 
    {
        return false;
    }

    // Return true if the CVV 
    // (Card Verification Value) number 
    // matched the ReGex
    if (regex_match(str, pattern)) 
    {
        return true;
    }
    else 
    {
        return false;
    }
}

// Driver Code
int main()
{
    // Test Case 1:
    string str1 = "561";
    cout << isValidCVVNumber(str1) << endl;

    // Test Case 2:
    string str2 = "5061";
    cout << isValidCVVNumber(str2) << endl;

    // Test Case 3:
    string str3 = "50614";
    cout << isValidCVVNumber(str3) << endl;

    // Test Case 4:
    string str4 = "5a#1";
    cout << isValidCVVNumber(str4) << endl;

    return 0;
}

// This code is contributed by yuvraj_chandra

// Java program to validate
// CVV (Card Verification Value)
// number using regex.
import java.util.regex.*;
class GFG {

    // Function to validate
    // CVV (Card Verification Value) number.
    // using regular expression.
    public static boolean isValidCVVNumber(String str)
    {
        // Regex to check valid CVV number.
        String regex = "^[0-9]{3,4}$";

        // Compile the ReGex
        Pattern p = Pattern.compile(regex);

        // If the string is empty
        // return false
        if (str == null) 
        {
            return false;
        }

        // Find match between given string
        // and regular expression
        // using Pattern.matcher()

        Matcher m = p.matcher(str);

        // Return if the string
        // matched the ReGex
        return m.matches();
    }

    // Driver code
    public static void main(String args[])
    {

        // Test Case 1:
        String str1 = "561";
        System.out.println(isValidCVVNumber(str1));

        // Test Case 2:
        String str2 = "5061";
        System.out.println(isValidCVVNumber(str2));

        // Test Case 3:
        String str3 = "50614";
        System.out.println(isValidCVVNumber(str3));

        // Test Case 4:
        String str4 = "5a#1";
        System.out.println(isValidCVVNumber(str4));
    }
}

# Python3 program to validate
# CVV (Card Verification Value)
# number using regex.
import re

# Function to validate
# CVV (Card Verification Value) number.
# using regular expression.


def isValidCVVNumber(str):

    # Regex to check valid
    # CVV number.
    regex = "^[0-9]{3,4}$"

    # Compile the ReGex
    p = re.compile(regex)

    # If the string is empty
    # return false
    if(str == None):
        return False

    # Return if the string
    # matched the ReGex
    if(re.search(p, str)):
        return True
    else:
        return False

# Driver code


# Test Case 1:
str1 = "561"
print(isValidCVVNumber(str1))

# Test Case 2:
str2 = "5061"
print(isValidCVVNumber(str2))

# Test Case 3:
str3 = "50614"
print(isValidCVVNumber(str3))

# Test Case 4:
str4 = "5a#1"
print(isValidCVVNumber(str4))

# This code is contributed by avanitrachhadiya2155

// C# program to validate the
// CVV (Card Verification Value) number
//using Regular Expressions
using System;
using System.Text.RegularExpressions;
class GFG
{

// Main Method
static void Main(string[] args)
{

    // Input strings to Match
    // CVV (Card Verification Value) number
    string[] str={"561","5061","50614","5a#1"};
    foreach(string s in str) {
    Console.WriteLine( isValidCVVNumber(s) ? "true" : "false");
    }
    Console.ReadKey(); }

// method containing the regex
public static bool isValidCVVNumber(string str)
{
    string strRegex = @"^[0-9]{3,4}$";
    Regex re = new Regex(strRegex);
    if (re.IsMatch(str))
    return (true);
    else
    return (false);
}
}

// This code is contributed by Rahul Chauhan

// Javascript program to validate
// CVV Number  using Regular Expression

// Function to validate the
// CVV_Number  
function isValid_CVV_Number(CVV_Number) {
    // Regex to check valid
    // CVV_Number  
    let regex = new RegExp(/^[0-9]{3,4}$/);

    // if CVV_Number 
    // is empty return false
    if (CVV_Number == null) {
        return "false";
    }

    // Return true if the CVV_Number
    // matched the ReGex
    if (regex.test(CVV_Number) == true) {
        return "true";
    }
    else {
        return "false";
    }
}

// Driver Code
// Test Case 1:
let str1 = "561";
console.log(isValid_CVV_Number(str1));

// Test Case 2:
let str2 = "5061";
console.log(isValid_CVV_Number(str2));

// Test Case 3:
let str3 = "50614";
console.log(isValid_CVV_Number(str3));

// Test Case 4:
let str4 = "5a#1";
console.log(isValid_CVV_Number(str4));

// Test Case 5:
let str5 = "12071998";
console.log(isValid_CVV_Number(str5));

// Test Case 6:
let str6 = "RAH12071998";
console.log(isValid_CVV_Number(str6));

// This code is contributed by Rahul Chauhan

true
true
false
false

Time Complexity: O(N) for each testcase, where N is the length of the given string. 
Auxiliary Space: O(1)