Write a Program in C++ to check whether the given Number is Prime or Composite Number.

Prime Number

A prime number is a number that can only be divided by itself and 1 without remainders. A prime number cannot be divided by any other numbers without leaving a remainder. An example of a prime number is 13. It can only be divided by 1 and 13. Dividing a prime number by another number results in numbers left over e.g. 13 ÷ 6 = 2 remainder 1.

Composite Number

Composite numbers can be defined as natural numbers that have more than two factors. In other words, a number that is divisible by a number other than 1 and the number itself, is called a composite number. 4, 6, 8, 9, and 10 are the first few composite numbers. Let's take 4 and 6. In the above example, 4 and 6 are called composite numbers because they are made by combining other numbers.

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()
{
//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:

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