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# C++ Determine if the Number is Prime or Composite

Hello Everyone!

In this tutorial, we will learn how to check if the given number if Prime or Composite, in the C++ programming language.

Code:

``````#include <iostream>
#include <math.h>

using namespace std;

//Returns true if the given number is a Prime number
bool isPrime(int n)
{
if (n == 1)
return false; // as 1 is not a prime number

for (int i = 2; i <= sqrt(n); i++) // Complexity O(SquareRoot(n))
{
if (n % i == 0)
return false;
}

return true;
}

int main()
{
cout << "\n\nWelcome to Studytonight :-)\n\n\n";
cout << " ===== Most Efficient Program to determine if the entered number is Prime or not. ===== \n\n";

cout << " ===== Note: 1 is neither Prime nor Composite. ===== \n\n";

//variable declaration
int n;
bool prime = false;

//taking input from the command line (user)
cout << " Enter a positive integer other than 1 :  ";
cin >> n;

//Calling a method that returns true if the number is Prime
prime = isPrime(n);

if (prime)
{
cout << "\n\nThe entered number " << n << " is a Prime number.";
}
else
{
cout << "\n\nThe entered number " << n << " is Composite number.";
}

cout << "\n\n\n";

return 0;
}
``````

Output:

Let's try with another input,

We hope that this post helped you develop a better understanding of how to check if given number is Prime or Composite, in C++. For any query, feel free to reach out to us via the comments section down below.

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