Prime Check
Program to check if a number is prime
BeginnerTopic: Loop Programs
C++ Prime Check Program
This program helps you to learn the fundamental structure and syntax of C++ programming.
#include <iostream>
#include <cmath>
using namespace std;
int main() {
int num;
bool isPrime = true;
cout << "Enter a number: ";
cin >> num;
if (num <= 1) {
isPrime = false;
} else {
for (int i = 2; i <= sqrt(num); i++) {
if (num % i == 0) {
isPrime = false;
break;
}
}
}
if (isPrime) {
cout << num << " is a prime number" << endl;
} else {
cout << num << " is not a prime number" << endl;
}
return 0;
}Output
Enter a number: 17 17 is a prime number
Understanding Prime Check
A prime number is only divisible by 1 and itself. We check divisibility from 2 to √n (square root optimization). If any number divides it, it's not prime. We only need to check up to √n because if a factor exists, one must be ≤ √n.
Note: To write and run C++ programs, you need to set up the local environment on your computer. Refer to the complete article Setting up C++ Development Environment. If you do not want to set up the local environment on your computer, you can also use online IDE to write and run your C++ programs.