C++ How To Check if a Number Is Prime
Check if a Number Is Prime
A prime number is larger than 1, and can only be divided by 1 and itself. Check if any smaller number divides it:
Example
int number = 29;
bool isPrime = true;
if (number < 2) {
isPrime = false;
}
for (int i = 2; i * i <= number; i++) {
if (number % i == 0) {
isPrime = false;
break;
}
}
if (isPrime) {
cout << number << " is a prime number";
} else {
cout << number << " is not a prime number";
}Explanation:
If number % i is 0, i divides the number, so it is not prime, and break stops the loop.
We only need to check up to the square root of the number (i * i <= number), which makes the check faster.
