Double Factorial without recursion, just a while loop

[strflyr]

I've got a very specific homework problem I am working on. I am supposed to find the semi or double factorial of any given positive integer. My program works fine with evens, but not odds. What am I missing?

int main(){
    
    unsigned long i, num, fact = 1;
    cout <<"enter integer: " << endl;
    cin >> num;
    i = num;
    while (num)
    {
        if (num == 0)
        {
            fact = 1;
            cout << "the double or semifactorial of " << i << " is " << fact << endl;
            return 1;
        }
        if (num == 1)
        {
            fact = 1;
            cout << "the double or semifactorial of " << i << " is " << fact << endl;
            return 1;
        }
        if (num % 2 == 0)
        {
        
        fact = fact * num;
        num = num - 2;
        }
        
        if (num % 2 != 0)
        {
            
            fact = (fact * num);
            num = (num - 2);
        }
    }
    cout << "the double or semifactorial of " << i << " is " << fact << endl;
}

[killingthemonkey]

I'd try something like this.

Note: It still breaks on the odd numbers. Working on it.

//doubleFactorial.cpp
//Take integer input and compute the double factorial
#include <iostream>
using std::cout;
using std::cin;
using std::endl;

int main(){
    
    unsigned long i, num, fact = 1;
    cout <<"enter integer: " << endl;
    cin >> num;
    i = num;
    
	if(num == 0)
		fact = 1;
	else if(num == -1)
		fact = 1;
	else if(num % 2 == 0 && num >= 2)
		while(num)
		{
			fact *= num;
			num -= 2;
		}
		
	else if(num % 2 !=0 && num >= 1)
		while(num >= 1)
		{
			fact *= num;
			num -= 2;
		}
		
    cout << "The double or semifactorial of " << i << " is " << fact << endl;
	
	return 0;
}

I sit here, pencil testing it, and I can't find my logic error. This code compiles without a hitch. Throw it an odd number and it just sits there, blinking a cursor at me... and laughing.