C++ code for checking for prime numbers not working

Question

I\'m having trouble with this C++ code. The integer num is a number that I want to check if it is prime. However this program is always returning false. It\'s proba

Answer 1

A small optimization for Will Ness's code, just calculate the sqrt of the number outside the for. The condition check executes many times and has no sense to calculate sqrt each time.

if( num == 2 ) return true;
if( num < 2 || num % 2 == 0 ) return false;
int sqrt = sqrt(num);

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

So far I think that this is the most efficient way!