Open In App

Composite Number

Improve
Improve
Like Article
Like
Save
Share
Report

A composite number is a positive integer that is not prime. In other words, it has a positive divisor other than one or itself. First few composite numbers are 4, 6, 8, 9, 10, 12, 14, 15, 16, 18, 20, ……… 
 

  • Every integer greater than one is either a prime number or a composite number.
  • The number one is a unit – it is neither prime nor composite.

How to check if a given number is a composite number or not? 
Examples: 
 

Input : n = 21
Output: Yes
The number is a composite number!

Input : n = 11
Output : No

 

The idea is simple, we can use any of the below methods used for prime checking. We just need to change return statements. Return true is changed to return false and vice versa. 
 

In below code optimized school method is discussed. 
 

C++




// A optimized school method based C++ program to check
// if a number is composite.
#include <bits/stdc++.h>
using namespace std;
   
bool isComposite(int n)
{
    // Corner cases
    if (n <= 1)  return false;
    if (n <= 3)  return false;
   
    // This is checked so that we can skip 
    // middle five numbers in below loop
    if (n%2 == 0 || n%3 == 0) return true;
   
    for (int i=5; i*i<=n; i=i+6)
        if (n%i == 0 || n%(i+2) == 0)
           return true;
   
    return false;
}
   
   
// Driver Program to test above function
int main()
{
    isComposite(11)?  cout << " true\n": cout << " false\n";
    isComposite(15)?  cout << " true\n": cout << " false\n";
    return 0;
}


Java




/// An optimized method based Java
// program to check if a number 
// is Composite or not.
import java.io.*;
  
class Composite
{
    static boolean isComposite(int n)
    {
        // Corner cases
        if (n <= 1
        System.out.println("False");
          
        if (n <= 3
        System.out.println("False");
  
        // This is checked so that we can skip 
        // middle five numbers in below loop
        if (n % 2 == 0 || n % 3 == 0) return true;
  
        for (int i = 5; i * i <= n; i = i + 6)
            if (n % i == 0 || n % (i + 2) == 0)
            return true;
  
        return false;
    }
  
    // Driver Program to test above function
    public static void main(String args[])
    {
        System.out.println(isComposite(11) ?
                       "true" : "false");
                         
        System.out.println(isComposite(15) ?
                       "true" : "false");
    }
}
  
// This code is contributed by Anshika Goyal


Python 3




# A optimized school method based Python program to check
# if a number is composite.
  
def isComposite(n):
  
    # Corner cases
    if (n <= 1):
        return False
    if (n <= 3):
        return False
  
    # This is checked so that we can skip 
    # middle five numbers in below loop
    if (n % 2 == 0 or n % 3 == 0):
        return True
    i = 5
    while(i * i <= n):
          
        if (n % i == 0 or n % (i + 2) == 0):
            return True
        i = i + 6
          
    return False
  
# Driver Program to test above function
  
print("true") if(isComposite(11)) else print("false")
print("true") if(isComposite(15)) else print("false")
# This code is contributed by Anant Agarwal.


C#




// A optimized school method based C# program 
// to check if a number is composite.
using System;
  
namespace Composite
{
public class GFG
{     
                  
    public static bool isComposite(int n)
    {
          
    // Corner cases
    if (n <= 1) return false;
    if (n <= 3) return false;
  
    // This is checked so that we can skip 
    // middle five numbers in below loop
    if (n % 2 == 0 || n % 3 == 0) return true;
  
    for (int i = 5; i * i <= n; i = i + 6)
      
        if (n % i == 0 || n % (i + 2) == 0)
        return true;
  
    return false;
    }
  
  
    // Driver Code
    public static void Main()
    {
          
    if(isComposite(11)) Console.WriteLine("true");
    else Console.WriteLine("false");
      
    if(isComposite(15)) Console.WriteLine("true");
    else Console.WriteLine("false");
    }
  
}
  
  
// This code is contributed by Sam007


PHP




<?php
// A optimized school 
// method based PHP
// program to check
// if a number is composite.
  
function isComposite($n)
{
      
    // Corner cases
    if ($n <= 1) 
        return false;
    if ($n <= 3) 
        return false;
  
    // This is checked so 
    // that we can skip 
    // middle five numbers 
    // in below loop
    if ($n%2 == 0 || $n % 3 == 0)
        return true;
  
    for ($i = 5; $i * $i <= $n;
                   $i = $i + 6)
        if ($n % $i == 0 || $n % ($i + 2) == 0)
        return true;
  
    return false;
}
  
    // Driver Code
    if(isComposite(11))
        echo "true";
        else
        echo "false";
        echo"\n";
    if(isComposite(15))
        echo "true";
        else
        echo "false";
        echo"\n";
      
// This code is contributed by Ajit. 
?>


Javascript




<script>
  
// A optimized school method based Javascript program to check 
// if a number is composite. 
  
function isComposite(n) 
    // Corner cases 
    if (n <= 1) return false
    if (n <= 3) return false
  
    // This is checked so that we can skip 
    // middle five numbers in below loop 
    if (n%2 == 0 || n%3 == 0) return true
  
    for (let i=5; i*i<=n; i=i+6) 
        if (n%i == 0 || n%(i+2) == 0) 
        return true
  
    return false
  
  
// Driver Program to test above function 
   
    isComposite(11)? document.write(" true" + "<br>"): document.write(" false" + "<br>"); 
    isComposite(15)? document.write(" true" + "<br>"): document.write(" false" + "<br>"); 
   
      
// This code is contributed by Mayank Tyagi
  
</script>


Output: 

false
true

Time Complexity:- O(sqrt(n))

Space Complexity:-O(1)
  
Program on Composite Numbers 
 

Reference : 
https://en.wikipedia.org/wiki/Composite_number

 



Last Updated : 29 Feb, 2024
Like Article
Save Article
Previous
Next
Share your thoughts in the comments
Similar Reads