How to check if a given number is Fibonacci number?

// C++ program to check if x is a perfect square
#include <iostream>
#include <math.h>
using namespace std;

// A utility function that returns true if x is perfect square
bool isPerfectSquare(int x)
{
    int s = sqrt(x);
    return (s*s == x);
}

// Returns true if n is a Fibinacci Number, else false
bool isFibonacci(int n)
{
    // n is Fibinacci if one of 5*n*n + 4 or 5*n*n - 4 or both
    // is a perferct square
    return isPerfectSquare(5*n*n + 4) ||
           isPerfectSquare(5*n*n - 4);
}

// A utility function to test above functions
int main()
{
  for (int i = 1; i <= 10; i++)
     isFibonacci(i)? cout << i << " is a Fibonacci Number \n":
                     cout << i << " is a not Fibonacci Number \n" ;
  return 0;
}

// Java program to check if x is a perfect square

class GFG
{
    // A utility method that returns true if x is perfect square
    static  boolean isPerfectSquare(int x)
    {
        int s = (int) Math.sqrt(x);
        return (s*s == x);
    }
     
    // Returns true if n is a Fibonacci Number, else false
    static boolean isFibonacci(int n)
    {
        // n is Fibonacci if one of 5*n*n + 4 or 5*n*n - 4 or both
        // is a perfect square
        return isPerfectSquare(5*n*n + 4) ||
               isPerfectSquare(5*n*n - 4);
    }

    // Driver method 
    public static void main(String[] args)
    {
        for (int i = 1; i <= 10; i++)
             System.out.println(isFibonacci(i) ?  i +  " is a Fibonacci Number" :
                                                  i + " is a not Fibonacci Number");
    }
}
//This code is contributed by Nikita Tiwari

# python program to check if x is a perfect square
import math

# A utility function that returns true if x is perfect square
def isPerfectSquare(x):
    s = int(math.sqrt(x))
    return s*s == x

# Returns true if n is a Fibinacci Number, else false
def isFibonacci(n):

    # n is Fibinacci if one of 5*n*n + 4 or 5*n*n - 4 or both
    # is a perferct square
    return isPerfectSquare(5*n*n + 4) or isPerfectSquare(5*n*n - 4)
   
# A utility function to test above functions
for i in range(1,11):
     if (isFibonacci(i) == True):
         print i,"is a Fibonacci Number"
     else:
         print i,"is a not Fibonacci Number "

// C# program to check if 
// x is a perfect square
using System;

class GFG {

    // A utility function that returns
    // true if x is perfect square
    static bool isPerfectSquare(int x)
    {
        int s = (int)Math.Sqrt(x);
        return (s * s == x);
    }

    // Returns true if n is a 
    // Fibonacci Number, else false
    static bool isFibonacci(int n)
    {
        // n is Fibonacci if one of
        // 5*n*n + 4 or 5*n*n - 4 or 
        // both are a perfect square
        return isPerfectSquare(5 * n * n + 4) || 
               isPerfectSquare(5 * n * n - 4);
    }

    // Driver method
    public static void Main()
    {
        for (int i = 1; i <= 10; i++)
            Console.WriteLine(isFibonacci(i) ? i + 
                              " is a Fibonacci Number" : i +
                              " is a not Fibonacci Number");
    }
}

// This code is contributed by Sam007