Passing parameters by reference in C++ - Mini Project: Build & Apply

Passing parameters by reference

📖 Scenario: Imagine you have a simple program that needs to update a number by doubling it. Instead of returning the new value, you want the original number to change directly when you call a function.

🎯 Goal: Build a C++ program that uses a function to double a number by passing the number by reference. This means the function will change the original number directly.

📋 What You'll Learn

Create an integer variable named num with the value 10.

Create a function named doubleValue that takes an integer parameter by reference.

Inside doubleValue, multiply the parameter by 2.

Call doubleValue with num as the argument.

Print the value of num after the function call.

💡 Why This Matters

🌍 Real World

Passing parameters by reference is useful when you want functions to modify data directly, such as updating settings, counters, or large data structures without copying them.

💼 Career

Understanding parameter passing is important for writing efficient and clear C++ code, which is a key skill in software development, game programming, and systems programming.

1

Create the initial variable

Create an integer variable called num and set it to 10.

C++

int num = 10;
// Your code here

Need a hint?

Use int num = 10; to create the variable.

2

Create the function with reference parameter

Create a function named doubleValue that takes an int parameter by reference named value. Inside the function, multiply value by 2.

C++

#include 

void doubleValue(int& value) {
    // Your code here
}

int main() {
    int num = 10;
    return 0;
}

Need a hint?

Use int& value to pass the parameter by reference.

3

Call the function with the variable

Inside main(), call the function doubleValue with the variable num as the argument.

C++

#include 

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

int main() {
    int num = 10;
    doubleValue(num);
    // Your code here
    return 0;
}

Need a hint?

Call the function by writing doubleValue(num); inside main().

4

Print the updated value

Add a std::cout statement inside main() to print the value of num after calling doubleValue. The output should be exactly 20.

C++

#include 

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

int main() {
    int num = 10;
    doubleValue(num);
    std::cout << num << std::endl;
    // Your code here
    return 0;
}

Need a hint?

Use std::cout << num << std::endl; to print the value.