# Find the Diameter or Longest chord of a Circle

Given a circle with radius ‘r’ is given, the task is to find the diameter or longest chord of the circle.**Examples:**

Input:r = 4Output:8Input:r = 9Output:18

**Proof that the Longest chord of a circle is its Diameter:**

- Draw circle O and any chord AB on it.
- From one endpoint of the chord, say A, draw a line segment through the centre. That is, draw a diameter.
- Now draw a radius from centre O to B.
- By the triangle inequality,

AB < AO + OB = r + r = 2r = d

- So, any chord that is not a diameter will be smaller than a diameter.
- So the largest chord is a diameter

**Approach**:

- The Longest chord of any circle is its diameter.
- Therefore, the diameter of a circle is twice the radius of it.

Length of the longest chord or diameter = 2r

Below is the implementation of the above approach:

## C++

`// C++ program to find` `// the longest chord or diameter` `// of the circle whose radius is given` `#include <bits/stdc++.h>` `using` `namespace` `std;` `// Function to find the longest chord` `void` `diameter(` `double` `r)` `{` ` ` `cout << ` `"The length of the longest chord"` ` ` `<< ` `" or diameter of the circle is "` ` ` `<< 2 * r << endl;` `}` `// Driver code` `int` `main()` `{` ` ` `// Get the radius` ` ` `double` `r = 4;` ` ` `// Find the diameter` ` ` `diameter(r);` ` ` `return` `0;` `}` |

## Java

`// Java program to find` `// the longest chord or diameter` `// of the circle whose radius is given` `class` `GFG` `{` ` ` `// Function to find the longest chord` `static` `void` `diameter(` `double` `r)` `{` ` ` `System.out.println(` `"The length of the longest chord"` ` ` `+ ` `" or diameter of the circle is "` ` ` `+ ` `2` `* r);` `}` `// Driver code` `public` `static` `void` `main(String[] args)` `{` ` ` ` ` `// Get the radius` ` ` `double` `r = ` `4` `;` ` ` `// Find the diameter` ` ` `diameter(r);` `}` `}` `// This code contributed by Rajput-Ji` |

## Python3

`# Python3 program to find` `# the longest chord or diameter` `# of the circle whose radius is given` `# Function to find the longest chord` `def` `diameter(r):` ` ` `print` `(` `"The length of the longest chord"` ` ` `,` `" or diameter of the circle is "` ` ` `,` `2` `*` `r)` `# Driver code` `# Get the radius` `r ` `=` `4` `# Find the diameter` `diameter(r)` `# This code is contributed by mohit kumar` |

## C#

`// C# program to find` `// the longest chord or diameter` `// of the circle whose radius is given` `using` `System;` `class` `GFG` `{` ` ` `// Function to find the longest chord` `static` `void` `diameter(` `double` `r)` `{` ` ` `Console.WriteLine(` `"The length of the longest chord"` ` ` `+ ` `" or diameter of the circle is "` ` ` `+ 2 * r);` `}` `// Driver code` `public` `static` `void` `Main(String[] args)` `{` ` ` ` ` `// Get the radius` ` ` `double` `r = 4;` ` ` `// Find the diameter` ` ` `diameter(r);` `}` `}` `// This code has been contributed by 29AjayKumar` |

## PHP

`<?php` `// PHP program to find` `// the longest chord or diameter` `// of the circle whose radius is given` `// Function to find the longest chord` `function` `diameter(` `$r` `)` `{` ` ` `echo` `"The length of the longest chord"` ` ` `,` `" or diameter of the circle is "` ` ` `,2 * ` `$r` `<< ` `"\n"` `;` `}` ` ` `// Driver code` ` ` `// Get the radius` ` ` `$r` `= 4;` ` ` `// Find the diameter` ` ` `diameter(` `$r` `);` ` ` ` ` `// This code is contributed by Ryuga` `?>` |

## Javascript

`<script>` `// javascript program to find` `// the longest chord or diameter` `// of the circle whose radius is given` ` ` `// Function to find the longest chord` `function` `diameter(r)` `{` ` ` `document.write(` `"The length of the longest chord"` ` ` `+ ` `" or diameter of the circle is "` ` ` `+ 2 * r);` `}` `// Driver code` ` ` `// Get the radius` `var` `r = 4;` `// Find the diameter` `diameter(r);` `// This code contributed by Princi Singh` `</script>` |

**Output:**

The length of the longest chord or diameter of the circle is 8