Program: Check given number for Prime Number

Program: Check given number for Prime Number

We know about prime number is a number which is greater than one and can only divide by 1 or by its own number. In this program we check the given number for prime number.

#include <iostream>

using namespace std;

int main() {

int n;

cout << "Enter Prime Number: ";

        cin >> n; //input number

//initialize flag for true assume given number is prime number

bool flag = true; 

//if number is less than 2 than its not a prime number according to def

if(n<2)

flag = false; 

else if(n == 2) // if n is 2 than its prime number

flag = true;

        else if(n%2 ==0)

              flag = false;

else{

/*

   Now we check n > 2 whether its prime or not. We check for 2 earlier because from now on we are gonna skip all even number as other than 2 there are no even prime number as all divisible by 2. So we start with 3 and check up to n with increment of two in one loop. So if any number less than n found divisible with n then set flag to false and break the loop.

*/

for(int i=3;i<n;i+=2){

if(n%i == 0)

{

flag = false;

 break;

}

}

}

//print output according to flag value

if(flag)

cout<<"It is a Prime Number";

else

cout<<"It is Not a Prime Number";

return 0;  //https://cplspls.blogspot.com

}

OUTPUT: