Python: Program keeps getting into a infinite loop when using float

Here is my original working program:

def num_rushes(required_height, rush_height_gain, back_sliding):
    current_height = 0
    rushes = 0
    while current_height < required_height:
        rushes += 1
        current_height += rush_height_gain
        if current_height >= required_height:
            break
        else:
            current_height -= back_sliding
    return rushes

print num_rushes(100, 15, 7)

What this program does it calculates how many "rushes" it takes until we reach the desired height (required_height), after each rush (rush_height_gain), we fall back by a given amount (back_sliding).

What I am trying to is after each rush, is multiply the height gained by 0.95 (we lose 5% of the rush each time).

As you can see below, what I have done is converted rush_height_gain to a float and then added the line rush_height_gain *= 0.95 into my while loop, however for some reason, which I cannot seem to figure out, I end up with an 开发者_如何学Goinfinite loop.

def num_rushes(required_height, rush_height_gain, back_sliding):
    current_height = 0
    rushes = 0
    rush_height_gain = float(rush_height_gain)
    while current_height < required_height:
        rushes += 1
        current_height += rush_height_gain
        if current_height >= required_height:
            break
        else:
            current_height -= back_sliding
        rush_height_gain *= 0.95
    return rushes

print num_rushes(100, 15, 7)

Any help as to why this occurs and how can I get my desired result would be greatly appreciated.

Cheers.

rush_high_gain gets smaller with each pass through the while-loop. But back_sliding stays constant. If enough passes are made through the loop (about 15), rush_height_gain may be less than backsliding. At that point current_height will get smaller and smaller, and you will never exit the loop.

If you temporarily add a print statement into your loop to show the values of relevant variables at each iteration, you'll see that because you keep shrinking rush_height_gain, it eventually becomes smaller than back_sliding. Once that happens, the object slides back further than it goes up at each step, so you wind up actually losing height. That means that if you haven't reached required_height by that point, you never will.

Probably the easiest solution is to change your loop condition to stop if current_height becomes negative, or alternatively if rush_height_gain becomes less than back_sliding. Alternatively, you could change the way you compute rush_height_gain so that it never becomes less than back_sliding.