C++ program to generate CAPTCHA and verify user

A CAPTCHA is a test to check whether the user is a human or not. CAPTCHA verification is very widely used to determine the user is a human or machine. In this article, we will implement a program that generates a CAPTCHA and we will verify it in C++.

Examples

Input: CAPTCHA: x97s72s
       user_input: x97s72s
Output: Valid CAPTCHA

Input: CAPTCHA: a67s89dP
       user_input: a76s89dP
Output: Invaild CAPTCHA

Generate CAPTCHA in C++

We are using rand() to generate CAPTCHA randomly.

1. Create a function generateCaptcha that generate a CAPTCHA of length n

• Create an empty string captcha to store the generated captcha.
• use rand() function to add characters to the captcha.

2. Now get the user input.

3. Use compare() function to compare the generated captcha with user input.

#include <bits/stdc++.h>
using namespace std;
// function to check user input to generated CAPTCHA
bool check_Captcha(string &captcha, string &user_input){
    return captcha.compare(user_input) == 0;
}
// function to generate CAPTCHA of length n
string generateCaptcha(int n){
    time_t t;
    srand((unsigned)time(&t));

    char *required_chars = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
    string captcha = "";
    while(n--)
        captcha.push_back(required_chars[rand()%62]);

    return captcha;
}
int main(){
    int n;
    cout<<"Enter the required length of CAPTCHA: ";
    cin>>n;
    string captcha = generateCaptcha(n);
    cout<<"CAPTCHA: "<<captcha<<endl;
    string user_input;
    cout<<"Enter the CAPTCHA: ";
    cin>>user_input;
    if (check_Captcha(captcha, user_input))
        cout<<"Valid CAPTCHA"<<endl;
    else
        cout<<"Invalid CAPTCHA"<<endl;

    return 0;
}

Output

Enter the required length of CAPTCHA: 6
CAPTCHA: OsBVxh
Enter the CAPTCHA: OsBVxh
Valid CAPTCHA

Enter the required length of CAPTCHA: 8
CAPTCHA: R5y3cVuW
Enter the CAPTCHA: R5y3cVuW
Valid CAPTCHA

Enter the required length of CAPTCHA: 5
CAPTCHA: Y3EgK
Enter the CAPTCHA: y3egk
Invalid CAPTCHA

Also, read

• Generate pseudo random numbers in C++
• How to compare between string in C++