How to Validate User Input in C++

//C++ Program to validate the data type of the input
#include <iostream>
#include <limits>
using namespace std;

int main() {
    int number;
    cout << "Enter an integer: ";
    while (!(cin >> number)) {
        cout << "Invalid input. Please enter an integer: ";
        cin.clear(); 
        cin.ignore(numeric_limits<streamsize>::max(), '\n');
    }
    cout << "You entered: " << number << endl;
    return 0;
}

//  C++ Program to validate the range of the input
#include <iostream>
#include <limits>
using namespace std;

int main() {
    int age;
    cout << "Enter your age (1-120): ";
    while (!(cin >> age) || age < 1 || age > 120) {
        cout << "Invalid input. Please enter an age between 0 and 120: ";
        cin.clear();
        cin.ignore(numeric_limits<streamsize>::max(), '\n');
    }
    cout << "You entered: " << age << endl;
    return 0;
}

// C++ Program to Validate String Format for emails using regular expressions
#include <iostream>
#include <string>
#include <regex>
using namespace std;

int main() {
    string email;
    regex email_pattern(R"((\w+)(\.{1}\w+)*@(\w+)(\.{1}\w+)+)");

    cout << "Enter an email address: ";
    getline(cin, email);

    if (!regex_match(email, email_pattern)) {
        cerr << "Invalid email format." << endl;
    } else {
        cout << "Valid email: " << email << endl;
    }

    return 0;
}

// C++ Program for Custom Validations
#include <iostream>
#include <string>
using namespace std;

bool isValidPassword(const string& password) {
    if (password.length() < 8) return false;
    bool hasLower = false, hasUpper = false, hasDigit = false;
    for (char ch : password) {
        if (islower(ch)) hasLower = true;
        if (isupper(ch)) hasUpper = true;
        if (isdigit(ch)) hasDigit = true;
    }
    return hasLower && hasUpper && hasDigit;
}
int main() {
    string password;
    cout << "Enter a password (at least 8 characters, including uppercase, lowercase, and a digit): ";
    cin >> password;
    while (!isValidPassword(password)) {
        cout << "Invalid password. Please enter a valid password: ";
        cin >> password;
    }
    cout << "You entered a valid password." << endl;
    return 0;
}