References

This lesson covers references, a safer way than pointers to handle an "alias" for a variable. It's for anyone searching "C++ reference usage."

A reference gives an existing variable a second name. Declare one in the form type& variableName = originalVariable;, and unlike a pointer, you can treat it as if you're operating on the original variable directly, without writing * or & every time.

The example uses a reference, int& value, as a function parameter, so changing the value inside the function also affects the caller's variable.

A common early mistake is not seeing the difference from a pointer. A reference can't be re-bound to a different variable once linked, and it also can't have a "points to nothing" state like nullptr. That makes it usable more safely than a pointer.

In real projects, references are used a lot when passing large data to a function — avoiding the cost of copying it, while still being able to modify the value.

📖 Reference code

#include <iostream>

void doubleValue(int& value) {
    value = value * 2;
}

int main() {
    int num = 10;
    doubleValue(num);
    std::cout << "Result: " << num << std::endl;
    return 0;
}

✍️ Your code

Type your code, then press "Run"

🧪 This site can't compile or run C++ directly, so it checks on the spot whether what you typed matches the reference code (scoring happens entirely in your browser — nothing is sent anywhere).