A function in C++ is a block of code that runs or performs a task when it is called. A data is passed to this function, known as the parameter(s) of the function.
Functions are used to perform operations and they are really important when we try to reuse a code. In simpler terms, once a function is defined or created in a code, it can be used many times in the same code.
To create a function in C++, we write or specify the name of the function followed by parenthesis ()
.
void myFunction(){
// block of code to be executed
}
In the above syntax, myFunction()
is the name of the function we created. void
means that the function does not return a value. // block of code to be executed
is a comment but will normally take the block of code we wish to perform using the function.
When we create a function, it is saved in order to be used later in a code whenever it is called. To call a function in C++, we write the name of the function followed by two parentheses ()
and a semicolon ;
.
In the below code, we’ll create a function myFunction()
, and use this function to perform a simple task: to print Hello World
when we call it later on in the code.
#include <iostream>using namespace std;// creating a functionvoid myFunction() {cout << "Hello World";}int main() {// calling the functionmyFunction();return 0;}
myFunction()
.Hello World
whenever we call it.Note: A function defined by a user, such as the function we created above,
myFunction()
, should come before themain()
function. Otherwise, it will result in an error.
#include <iostream>using namespace std;// calling the main() function before the user-defined functionint main() {myFunction();return 0;}void myFunction() {cout << "I just got executed!";}// this will return an error message
The above code shows that when we declare the main()
function before a user-defined function, it ultimately returns an error message.