C++ function

We have already encountered one function named main. It is special function called at the beginning of the program.

Use of function

Example : Suppose we want to write a program to compute the area of three triangles. We could write out the formula three times or we could create a functionto do the work.

Syntax:

// defining function
function_type function_name(parameters)
{
    // statement(s)
}

// calling function
function_name(arguments);

• function_type is the data type of the data that function will return and if the written type is void then no data will be returned.
• function_name follows the same rules as variable name. This is not a coincidence, because both function and variable names are Identifier.
• parameters is a variable in a function definition. Parameters are optional.
• When a function is called, the arguments are the data passed into the function's parameters.

Example with parameters

#include<iostream>

using namespace std;

float triangle(float width,float height)
{
    float area;
    // area of triangle
    area = width * height / 2.0;

    return area;
}
int main()
{
    cout<<"Triangle #1 : "<< triangle(1.3,4.7) <<endl;
    cout<<"Triangle #2 : "<< triangle(4.1,2.1) <<endl;
    cout<<"Triangle #3 : "<< triangle(6.7,4.3) <<endl;

    return 0;
}

Output

Triangle #1 : 3.055
Triangle #2 : 4.305
Triangle #3 : 14.405

Example without parameter

#include <iostream>
using namespace std;

void area()
{
    float area_circle;
    float rad;

    cout<<"\nEnter the radius : ";
    cin>>rad;

    area_circle = 3.14 * rad * rad ;

    cout<<"\nArea of Circle = "<<area_circle;
}

int main()
{
    area();

    area();

    return 0;
}

Output

Enter the radius :
Area of Circle = 78.5
Enter the radius :
Area of Circle = 113.04