Question

I’ve beeen trying to get a program written for a lab for class, and I believe I almost have it, but it won’t add up the divisors (div in the code) to the sum and return true if it is a perfect number and false otherwise. My code compiles and runs fine but will only return a false, presumably because sum is staying at 1 (it initializes at one since 1 is a divisor of every number). number is a private int brought in from the constructors and set statements.

  public boolean isPerfect()
  {
    int x = number -1 ;
    int div = 0;
    int sum = 1;
    while(x> 1)
    {
        if(number % x == 0)
        {
            div =  x;
            sum=+ div;
        }
        x--;
    }
    if(sum == number)
    {
        return true;
    }
    else
    {
        return false;
    }
  }

Answer 1

As well as the += / =+ issue, your code also says that 1 is a perfect number, which is incorrect (6 is the first perfect number). This is because you start with a sum of 1, the loop won’t execute at all, then you compare sum and number, which are equal for 1. You could just add a check for this special case, e.g.

if(sum == number && number > 1)...

Additional tip – instead of :

if(sum == number)
{
    return true;
}
else
{
    return false;
}

You can just use:

return (sum == number);