如何修复在While循环中不更新的变量（Python）

Question

I am making a program that guesses a number that you are thinking of by telling the program if the number is higher or lower. I'm not getting errors, but I can't seem to update the variable "guess" in the while loop, it remains equal to 50. The formula for higher-lower is given by the textbook, so I can't change that.

I have tried moving the variable inside of the while loop, but still, it does not update.

print('Hello.')
print('Pick a secret number between 0 and 100.')
low = 0
high = 101
guess = 50
while True:
    print('Is your secret number',guess)
    use = input('Enter yes/higher/lower:\n').lower()
    if use == 'yes':
        print('Great!')
        break
    elif use == 'higher':
        low = guess
        guess = (guess-low)//2+low
    elif use == 'lower':
        high = guess
        guess = (high-guess)//2+guess
    else:
        print('I did not understand.')

Answer 1

IIUC, low , high , and guess needs to be updated for each loop. Your new guess should be the mean of your new low and high .

As is, your guess remains the same. For instance if the user responds with 'higher' , guess-low is 0 . Divide by 2 is still 0 , then add by low , which is guess .

You likely want this:

low = guess
guess = (high + low) // 2

and

high =  guess
guess = (high + low) // 2

Answer 2

That's weird, because there's something wrong with your formula.

    elif use == 'higher':
        low = guess
        guess = (guess-low)//2+low
    elif use == 'lower':
        high = guess
        guess = (high-guess)//2+guess

In this part, since low == high == guess , the result of guess - low and high - guess will always be 0. Dividing that by 2 also gives 0. Therefore, both lines become equivalent to guess = guess .

This is because you are reassigning to low and high , which I believe you mean to hold the lower and upper limits of the guessing range.

Perhaps you mean guess += (high - guess) // 2 and guess -= (guess - low) // 2 ?

Answer 3

Your problem seems to be variable 'value reallocation' (I'm not sure for this word I'm French), with Equals :

=

you must use

guess += value

or

guess = guess + guess

or

guess = guess - guess

or

guess -= guess

Answer 4

That's because the logic you used is wrong.

Right now, what's happening is,

low = guess
guess = (guess - low) // 2 + low

As low = guess the above statement is equivalent to,

guess = (guess - guess) // 2 + low
# guess = 0 + low
# guess = low

Similarly, for high,

high = guess
guess = (high - guess) //2 + guess

As high = guess the above statement is equivalent to,

guess = (high - high) // 2 + guess
# guess = 0 + guess
# guess = guess

That's why it's always stuck on 50 .

---

The actual logic for it to work is as follows,

elif use == 'higher':
    low = guess
    guess = (guess + high) // 2
elif use == 'lower':
    high = guess
    guess = (guess + low) // 2

Change the snippet to this. It will work!

---

Hope this helps! :)