C++ Functions

Functions

Functions allow to structure programs in segments of code to perform individual tasks.

In C++, a function is a group of statements that is given a name, and which can be called from some point of the program. The most common syntax to define a function is:

type name ( parameter1, parameter2, ...) { statements }




Let's have a look at an example:

// function example
#include <iostream>
using namespace std;

int addition (int a, int b)
{
  int r;
  r=a+b;
  return r;
}
int main ()
{
  int z;
  z = addition (5,3);
  cout << "The result is " << z;
}

The result is 8

This program is divided in two functions: addition and main. Remember that no matter the order in which they are defined, a C++ program always starts by calling main. In fact, main is the only function called automatically, and the code in any other function is only executed if its function is called from main (directly or indirectly).

A function can actually be called multiple times within a program, and its argument is naturally not limited just to literals:

// function example
#include <iostream>
using namespace std;

int subtraction (int a, int b)
{
  int r;
  r=a-b;
  return r;
}

int main ()
{
  int x=5, y=3, z;
  z = subtraction (7,2);
  cout << "The first result is " << z << '\n';
  cout << "The second result is " << subtraction (7,2) << '\n';
  cout << "The third result is " << subtraction (x,y) << '\n';
  z= 4 + subtraction (x,y);
  cout << "The fourth result is " << z << '\n';
}

The first result is 5
The second result is 5
The third result is 2
The fourth result is 6

Similar to the addition function in the previous example, this example defines a subtract function, that simply returns the difference between its two parameters. This time, main calls this function several times, demonstrating more possible ways in which a function can be called.

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