Defining functions
- C++ course
- Beginner
- Lesson 65/116
- 4 min
Learn how to define and call a function.
What is a function?
A function is a named, reusable block of code. You define it once and call it as many times as you like. The definition void greet() { std::cout << "hi"; } creates a function named greet.
Every function has a signature: return type, name and parameter list. The signature of void greet() reads 'greet, no parameters, returns nothing'. To call it you write its name followed by parentheses: greet();. This runs the code inside the function.
Definition vs call
The definition and the call of a function are different things. The definition says what the function does: void greet() { std::cout << "hi"; }. The call runs it: greet();.
In C++ the call can sit below or above the definition; as long as the compiler sees the definition, order does not matter. For readability it is common to place definitions before main. You can call a function many times; each call runs the same code again.
Practice Define greet and call it
Define a void greet() function whose body is std::cout << "hi" << std::endl;. Call it from main.
Starter code
#include <iostream>
// Define greet here
int main() {
// Call greet
return 0;
}Sample solution
#include <iostream>
void greet() {
std::cout << "hi" << std::endl;
}
int main() {
greet();
return 0;
}Expected output
hi
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What do you write to call a function?
void greet() { std::cout << "hi"; }- greet;
- greet(); Correct answer
- call greet();
- greet->();
Explanation: greet(); runs the function.
2 Complete the function call
greet____;greet();Explanation: greet() calls the function.
3 Match the function parts
| Term | Meaning |
|---|---|
void |
Return type |
greet |
Function name |
() |
Parameter list |
greet(); |
Call |