An account with its own errors – C++ Practice Problem

Define your own error types and handle them differently.

What to build

Two exception classes, thrown by one function and handled by its caller.

Requirements

Define BadAmount and NotEnough, both derived from runtime_error.
deposit X and withdraw X change a balance that starts at 0.
An amount of 0 or less throws BadAmount, and refused: bad amount is printed.
Withdrawing more than the balance throws NotEnough, and refused: not enough is printed.
At the end, print balance B.

Input

The first line has n. Each of the next n lines is a command.

Output

One line per refusal, then the balance.

Constraints

n is from 1 to 100. Amounts are from -1000 to 100000.

Example

Input:

3
deposit 100
withdraw 150
withdraw 30

Output:

refused: not enough
balance 70

Why it works

Each exception type names one problem, so that the handlers stay simple and a new kind of error can be added without changing the others.

Examples

Example 1 · Input

3
deposit 100
withdraw 150
withdraw 30

Expected output

refused: not enough
balance 70

Example 2 · Input

2
deposit -5
withdraw 0

Expected output

refused: bad amount
refused: bad amount
balance 0

Hints

Hint 1

Derive each error from runtime_error, and pass a message to its constructor.

Hint 2

Catch the specific types before the general one.

Hint 3

Throw from the function, and catch in main.

Solution

Show one correct solution (try it yourself first)

#include <iostream>
#include <stdexcept>
#include <string>
using namespace std;

class BadAmount : public runtime_error {
public:
    BadAmount() : runtime_error("bad amount") {}
};

class NotEnough : public runtime_error {
public:
    NotEnough() : runtime_error("not enough") {}
};

void apply(const string& command, int amount, int& balance) {
    if (amount <= 0) throw BadAmount();
    if (command == "deposit") {
        balance += amount;
    } else {
        if (amount > balance) throw NotEnough();
        balance -= amount;
    }
}

int main() {
    int n, balance = 0;
    cin >> n;
    for (int i = 0; i < n; i++) {
        string command;
        int amount;
        cin >> command >> amount;
        try {
            apply(command, amount, balance);
        } catch (const runtime_error& e) {
            cout << "refused: " << e.what() << endl;
        }
    }
    cout << "balance " << balance << endl;
    return 0;
}

Lesson: Exceptions and files →