CPP

check prime number c++

bool prime(int a) { 
    if (a < 2)
        return false;
    for (int i = 2; i * i <= a; i++) {
        if (a % i == 0)
            return false;
    }
    return true;
}

how to check if a number is prime c++

bool isPrime(int number){

    if(number < 2) return false;
    if(number == 2) return true;
    if(number % 2 == 0) return false;
    for(int i=3; (i*i)<=number; i+=2){
        if(number % i == 0 ) return false;
    }
    return true;

}

fast way to check if a number is prime C++

//O(sqrt(n))
bool isPrime(int num){
    if(num <= 1) return false;
    for(int i = 2; i <= sqrt(num); i++){
          if(num % i == 0) return false;
    }
    return true;
}