The void Keyword in C++

In C++, void is a special data type used primarily to indicate that a function does not return a value. It plays a critical role in defining function signatures and pointers. Though it is not a type used to declare regular variables, it is an important concept for structuring meaningful functions in your programs.

Where is void used?

The keyword void is used in three primary ways:

1. To indicate a function returns nothing
2. To declare a function that takes no parameters
3. To declare void pointers (advanced topic)

We’ll focus on the first two in beginner-level contexts.

1. Void as a Return Type

When a function does not return any value, it must be declared with void as the return type.

#include <iostream>
 
void greet() {
    std::cout << "Hello, welcome to C++!" << std::endl;
}
 
int main() {
    greet(); // Calling the function
    return 0;
}

• void greet() means this function doesn’t return anything.
• It simply performs an action (printing) and exits.

2. Void in Parameter List

When a function does not take any arguments, you can explicitly mention void in the parameter list:

#include <iostream>
 
void showCredits(void) {
    std::cout << "Created by: Your Name" << std::endl;
}
 
int main() {
    showCredits();
    return 0;
}

Note: Writing void inside the parentheses is optional in C++, but helps clarify the intent.

3. When Not to Use void

You cannot use void to declare a regular variable:

// ❌ This will cause an error
void x;  // Error: ‘x’ declared as void

Only functions and pointers (more advanced) can use void meaningfully.

Practical Example 1: Display Menu

A void function is great for displaying menus or information that doesn’t require returning any data.

#include <iostream>
 
void showMenu() {
    std::cout << "1. Start Game\n";
    std::cout << "2. Load Game\n";
    std::cout << "3. Exit\n";
}
 
int main() {
    showMenu();
    return 0;
}

Practical Example 2: Welcome Message

Use a void function to reduce repetition in your code by reusing a print block.

#include <iostream>
 
void welcome() {
    std::cout << "=====================" << std::endl;
    std::cout << "   Welcome to C++    " << std::endl;
    std::cout << "=====================" << std::endl;
}
 
int main() {
    welcome();
    return 0;
}

Practice Problem 1: Print Stars

Write a void function to print a line of 10 asterisks (*).

#include <iostream>
 
void printStars() {
    for (int i = 0; i < 10; i++) {
        std::cout << "*";
    }
    std::cout << std::endl;
}
 
int main() {
    printStars();
    return 0;
}

Practice Problem 2: Personalized Message

Write a function void greetUser(string name) that prints "Hello, <name>!".

#include <iostream>
 
void greetUser(std::string name) {
    std::cout << "Hello, " << name << "!" << std::endl;
}
 
int main() {
    greetUser("Alice");
    return 0;
}

Summary

The void keyword may seem simple, but it is fundamental to writing structured and clean C++ code. It separates actions from calculations and improves code readability and reusability.