Summary - Exceptions
- C++ course
- Beginner
- Lesson 105/116
- 5 min
Combine try/catch and a custom exception to write a bank account class.
Summary: Bank account
In this summary we will combine try/catch, throw and a custom exception to build a small bank account class. The Account class holds deposit and withdraw methods; if the balance is insufficient, an InsufficientFunds exception is thrown.
The plan: first derive the InsufficientFunds class from std::exception, then define the Account class with a balance member. The withdraw method throws if the amount exceeds the balance; the caller catches it with try/catch and reads the message via e.what(). This combines the exception tools in a real scenario.
Practice InsufficientFunds and withdraw
Add #include <stdexcept>. Define class InsufficientFunds : public std::exception; in a public: block write const char* what() const noexcept override { return "insufficient balance"; }. In main, add try { throw InsufficientFunds(); } catch (const std::exception& e) { cout << e.what() << endl; }.
Starter code
#include <iostream>
#include <stdexcept>
using namespace std;
// Define the InsufficientFunds class
int main() {
// in try throw, in catch print the message
return 0;
}Sample solution
#include <iostream>
#include <stdexcept>
using namespace std;
class InsufficientFunds : public std::exception {
public:
const char* what() const noexcept override {
return "insufficient balance";
}
};
int main() {
try {
throw InsufficientFunds();
} catch (const std::exception& e) {
cout << e.what() << endl;
}
return 0;
}Expected output
insufficient balance
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Match each tool with its job
| Term | Meaning |
|---|---|
try |
risky operation |
throw |
throws an exception |
InsufficientFunds |
custom exception |
2 What should the withdraw method do when the balance is insufficient?
- Crash
- Throws InsufficientFunds Correct answer
- Returns 0
- Ignores
Explanation: On insufficient balance, InsufficientFunds is thrown.
3 Fill in the blank: derivation
class InsufficientFunds : public ____ {
public:
const char* what() const noexcept override;
};class InsufficientFunds : public std::exception {
public:
const char* what() const noexcept override;
};Explanation: std::exception is used as the base class.