Unreachable Code Detected (Why?)

Question

So, why is it that there is unreachable code detected in this code:

      public bool GetKeyPressed(KeyCode key)
    {
        for (int i = 0; i < keys.Count; i++)
            if (keys[i].key == key && keys[i].pressed)
                return true;
            else
                return false;

        return false;
    }

The index (i) is apparently unreachable ... why?

Answer 1

Your code has a loop that evaluates once, therefore the first iteration will always return.

If that's what you want, just say that,

return keys[0].key == key && keys[0].pressed;

If however (which is what I suspect here), you want to return true if any in the array meets your test, then use LINQ's Any(),

return keys.Any(k => k.key == key && k.pressed);

Answer 2

Your code having two code path, one is through if condition and another is through the else. Which means the control will leave the function in these two ways. So the return statement after else will never triggers. That is why the compiler points it as unreachable code. This can be avoided by using the following code.

public bool GetKeyPressed(KeyCode key)
{
    for (int i = 0; i < keys.Count; i++)
        if (keys[i].key == key && keys[i].pressed)
            return true;          
        return false;
}

Answer 3

Expanding on jdphenix answer, I think we need to understand why your loop "evaluates once" and only then can we understand why there is "unreachable code".

public bool GetKeyPressed(Keys key)
{
    for (int i = 0; i < keys.Count; i++)
        if (keys[i].key == key && keys[i].pressed)
            return true;
        else
            return false;

    return false;
}

The for loop has a single if-else statement that makes up the body. The if guard if satisfied returns true otherwise it executes the next else statement which returns false. The net result is that at most a single cycle of the loop will be executed before control is returned to the calling method irrespective of the number of items in keys.

It's more obvious if we look at the code via JetBrains Resharper:

The code may as well be written as:

public bool GetKeyPressed(Keys key)
{
    for (int i = 0; i < keys.Count; ) // Look Ma, no i++  !!!
        if (keys[i].key == key && keys[i].pressed)
            return true;
        else
            return false;

    return false;
}

Don't make the mistake of thinking that the very last return false at the end of the method is not required because it is during the scenario where keys.Count == 0

Of course, formatting the code a bit more nicely goes a long way into revealing the problem that the first return false is redundant and could be simplified as per un-lucky's answer: