21 Jan C++ Functions

In this lesson, learn C++ Functions. A function is an organized block of reusable code, which avoids repeating the tasks again and again. If you want to do a task repeatedly in a code, then just make a function, set the task in it, and call the function multiple times whenever you need it.

Create and call a Function

To create a function in C++, set the name of the function followed by parentheses:

void demoFunction() {
  // write the code
}

A function in C++ gets executed when it is called:

demoFunction()

Let us now see an example to create a function in C++:

#include <iostream>
using namespace std;
 
// Demo function
void demoFunction() {

  cout<<"This is a demo function in C++.\n";
}
 
int main() {
 
  // Calling the function
  demoFunction();
  
  return 0;
}

Output

This is a demo function in C++.

Function Declaration and Definition

In the above example, we saw how to create and call a function in C++. We defined and declared the function as well:

void demoFunction() { // function declaration
  // function body i.e., the definition
}

As shown above, a function has two parts:

• Function Declaration
• Function Definition

We can also write the above C++ function by separating function definition and declaration. Let us see an example:

#include <iostream>
using namespace std;
  
// Function Declaration
void demoFunction();
 
int main() {
 
  // Calling the function
  demoFunction();
  
  return 0;
}
 
// Function Definition
void demoFunction() {
  
  cout<<"This is a demo function.\n";
}

Output

This is a demo function in C++.

Function Parameters

Set the parameters in a C++ function after the name of the function. For example:

void demoFunction(int rank) { }

To call a function with a parameter, set the value of the variable while calling, for example:

demoFunction(2)

Therefore, we have passed the rank with the value 2 while calling above.

Let us now see an example:

#include <iostream>
using namespace std;
 
// Function with a parameter
void detailsFunc(int rank) {
  cout<<"Rank = "<<rank;
}
 
int main() {
 
  // Calling the function
  detailsFunc(2);
  
  return 0;
}

Output

Rank = 2

Multiple Parameters

We can also set more than one parameter in a function in C++. For example:

void demoFunction(string player, int rank, int points) { }

To call a function with multiple parameters, set the value of the variable while calling, for example:

demoFunction("Amit", 1, 90)

We have passed the following multiple parameters while calling above:

• player: Amit
• rank: 1
• points: 90

Let us now see an example:

#include <iostream>
using namespace std;
 
// Function with multiple parameters
void detailsFunc(string player, int rank, int points) {
   cout<<"\nPlayer = "<<player;
   cout<<"\nRank = "<<rank;
   cout<<"\nPoints = "<<points<<"\n";
}
 
int main() {
 
  // Calling the function
  detailsFunc("Amit", 1, 90);
  detailsFunc("Jack", 2, 85);
  
  return 0;
}

Output

Player = Amit
Rank = 1
Points = 90
Player = Jack
Rank = 2
Points = 85