Program to calculate Area Of Octagon

A regular octagon is a closed figure with sides of the same length and internal angles of the same size. It has eight lines of reflective symmetry and rotational symmetry of order 8. The internal angle at each vertex of a regular octagon is 135°. The central angle is 45°.
Properties : 

Convex polygon, Equilateral polygon, Isogonal figure, Isotoxal figure, Cyclic.

Formula :

Area : 2 × (side length)² × (1+sqrt(2))

Examples :

Input : side = 3
Output : Area of Regular Octagon = 43.4558

Input : side = 4
Output : Area of Regular Octagon = 77.2548

C++

// CPP program to find area of octagon
#include <bits/stdc++.h>
using namespace std;

// Utility function
double areaOctagon(double side)
{
    return (float)(2 * (1 + sqrt(2)) *
                   side * side);
}

// Driver Code
int main()
{
    double side = 4;
    cout << "Area of Regular Octagon = "
         << areaOctagon(side) << endl;
    return 0;
}

Java

// Java Program to find
// area of Octagon.
import java.io.*;

class GFG
{
    // utility function
    static double areaOctagon(double side)
    {
    return (float)(2 * (1 + Math.sqrt(2))
                          * side * side);
    }

    // driver code
    public static void main(String arg[])
    {
        double side = 4;
        System.out.print("Area of Regular Octagon = "
                          + areaOctagon(side));
    }
}

// This code is contributed by Anant Agarwal.

Python3

# Python3 program to
# find area of octagon

import math

# Utility function
def areaOctagon(side):
    return (2 * (1 + (math.sqrt(2))) * side * side)

# Driver function
side = 4
print("Area of Regular Octagon =",
       round(areaOctagon(side), 4))

# This code is contributed
# by Azkia Anam.

C#

// C# Program to find
// area of Octagon.
using System;

class GFG
{
    // utility function
    static double areaOctagon(double side)
    {
    return (float)(2 * (1 + Math.Sqrt(2))
                        * side * side);
    }

    // Driver code
    public static void Main()
    {
        double side = 4;
        Console.WriteLine("Area of Regular Octagon = "
                          + areaOctagon(side));
    }
}

// This code is contributed by vt_m.

PHP

<?php
// PHP program to find area of octagon

// Utility function
function areaOctagon( $side)
{
    return (2 * (1 + sqrt(2)) *
            $side * $side);
}

// Driver Code

$side = 4;
echo("Area of Regular Octagon = ");
echo(areaOctagon($side));

// This code is contributed by vt_m.
?>

Javascript

<script>

// Javascript program to find area of octagon

// Utility function
function areaOctagon(side)
{
    return (2 * (1 + Math.sqrt(2)) *
                side * side);
}

// Driver Code
    let side = 4;
    document.write("Area of Regular Octagon = "
        + areaOctagon(side) + "<br>");

// This code is contributed by Mayank Tyagi
</script>

Output :

Area of Regular Octagon = 77.25

Time complexity : O(1) 
Auxiliary Space : O(1)