showing o/p in c: Error: Command failed: timeout 7 ./HelloWorld

You need to make sure, you provide STDIN as the program is taking two inputs.
Otherwise the program will wait and timeout eventually

Check this https://onecompiler.com/c/3x8wmck9r

Update: Unfortunately OneCompiler does not show as you are expecting. I have updated the code to show it in best possible way.

Thanx a lot,for Ur very very kind and fast help and answer.
But, i want to input from kb like below:

enter a: 5
enter b: 10
addition is 15

Thanx a lot.

#include <iostream>
#include <unordered_map>
#include <limits>
#include <string>

using namespace std;

// Structure to store account details
struct Account {
string password;
double balance;
};

// Global map to store user accounts
unordered_map<string, Account> accounts;

// Function to clear input stream
void clearInputStream() {
cin.clear();
cin.ignore(numeric_limits<streamsize>::max(), '\n');
}

// Function to create a new bank account
void createAccount() {
string userId, password;
cout << "Enter a new user ID: ";
cin >> userId;

if (accounts.find(userId) != accounts.end()) {
    cout << "User ID already exists. Please choose a different ID." << endl;
    return;
}

cout << "Enter a new password: ";
cin >> password;

accounts[userId] = {password, 0.0};
cout << "Account created successfully!" << endl;

}

// Function to login with user ID and password
string login() {
string userId, password;
cout << "Enter your user ID: ";
cin >> userId;

auto it = accounts.find(userId);
if (it == accounts.end()) {
    cout << "User ID not found. Please try again." << endl;
    return "";
}

cout << "Enter your password: ";
cin >> password;

if (it->second.password == password) {
    cout << "Login successful!" << endl;
    return userId;
} else {
    cout << "Incorrect password. Please try again." << endl;
    return "";
}

}

// Function to withdraw money from account
void withdrawMoney(Account& acc) {
double amount;
cout << "Enter the amount to withdraw: ";
cin >> amount;

if (amount > acc.balance) {
    cout << "Insufficient funds." << endl;
} else {
    acc.balance -= amount;
    cout << "Withdrawal successful. New balance: $" << acc.balance << endl;
}

}

// Function to deposit money into account
void depositMoney(Account& acc) {
double amount;
cout << "Enter the amount to deposit: ";
cin >> amount;

acc.balance += amount;
cout << "Deposit successful. New balance: $" << acc.balance << endl;

}

// Function to request balance of the account
void requestBalance(const Account& acc) {
cout << "Your current balance is: $" << acc.balance << endl;
}

// Main menu function for logged-in users
void mainMenu(const string& userId) {
while (true) {
cout << "\nMain Menu:" << endl;
cout << "1) Withdraw money" << endl;
cout << "2) Deposit money" << endl;
cout << "3) Request balance" << endl;
cout << "4) Quit" << endl;
cout << "Choose an option: ";

    int choice;
    cin >> choice;
    clearInputStream();  // Clear input stream to handle invalid input

    auto it = accounts.find(userId);
    if (it == accounts.end()) {
        cout << "User account not found!" << endl;
        return;
    }
    Account& acc = it->second;

    switch (choice) {
        case 1:
            withdrawMoney(acc);
            break;
        case 2:
            depositMoney(acc);
            break;
        case 3:
            requestBalance(acc);
            break;
        case 4:
            cout << "Quitting..." << endl;
            return;
        default:
            cout << "Invalid choice. Please try again." << endl;
    }
}

}

// Introduction menu function
void introductionMenu() {
while (true) {
cout << "\nIntroduction Menu:" << endl;
cout << "1) Create a bank account" << endl;
cout << "2) Login" << endl;
cout << "3) Quit" << endl;
cout << "Choose an option: ";

    int choice;
    cin >> choice;
    clearInputStream();  // Clear input stream to handle invalid input

    switch (choice) {
        case 1:
            createAccount();
            break;
        case 2:
            {
                string userId = login();
                if (!userId.empty()) {
                    mainMenu(userId);
                }
            }
            break;
        case 3:
            cout << "Quitting..." << endl;
            return;
        default:
            cout << "Invalid choice. Please try again." << endl;
    }
}

}

// Main function
int main() {
introductionMenu();
return 0;
}