* 1.0在此代码中做了什么？

Question

Here is a code for checking if a number is prime or not :

bool IsPrime(int num)
{
    if(num<=1)
        return false;
    if(num==2)
        return true;
    if(num%2==0)
        return false;
    int sRoot = sqrt(num*1.0);
    for(int i=3; i<=sRoot; i+=2)
    {
        if(num%i==0)
            return false;

    }
    return true;
}

What does the expression " num*1.0 " mean ?

Answer 1

Multiplying by 1.0 forces the num into a double . You can do the same with an explicit cast.

Answer 2

它正在执行num x 1.0，所以如果num是5，则它是5 x 1.0，sqrt（）方法需要double作为其参数，并且需要5.0

Answer 3

In num*1.0 , num is promoted to double first, so the result is a double and then pass to double sqrt(double) . Otherwise, you may need to use sqrt(static_cast<double>(num)) .

Generally, you don't need the cast because there is an implicit cast from int to double . Refer to here .