如何使用信号值在while循环中平均用户输入？

Question

For a classroom assignment I have been asked to create a program that averages a number of user input exam grades using a while loop. I have come up with a functioning program, however it does not meet the specific criteria required by my instructor. I need to Use a while-loop to allow the user to enter any number of exam scores, one number per line, until a sentinel value is entered. How might I alter this program to get the same result using a while loop and a sentinel value of 9999?

here is what I have so far.

scores=int(input("how many test scores will you enter: "))
total_sum=0
for n in range(scores):
    numbers=float(input("Enter exam score : "))
    total_sum+=numbers
avg=total_sum/scores
print("average of ", scores, " test scores is :", avg)

The output should look something like this

Enter exam score. 9999 to quit: 100
Enter exam score. 9999 to quit: 95.5
Enter exam score. 9999 to quit: 90
Enter exam score. 9999 to quit: 9999

These 3 scores average to : 95.16666667

Answer 1

Think the best way to do it would be store the scores in a list and then compute the average of them after the user enters the sentinel value:

SENTINEL = float(9999)

scores = []
while True:
    number = float(input("Enter exam score (9999 to quit): "))
    if number == SENTINEL:
        break
    scores.append(number)

if not scores:
    print("You didn't enter any scores.")
else:
    avg = sum(scores)/len(scores)
    print("average of ", len(scores), " test scores is :", avg)

Answer 2

There are a couple ways to go about this. The general approach would be to keep a running total of the scores, as well as how many scores you've read, and then check whether the next score to read is == 9999 to see whether or not to exit the while loop.

A quick version might be the following:

num_scores = 0
total_sum = 0
shouldExit = False
while shouldExit is False:
    nextScore = float(input("Enter exam score : "))
    if nextScore == 9999: #find a way to do this that does not involve a == comparison on a floating-point number, if you can
        shouldExit = True
    if shouldExit is False:
        num_scores += 1
        total_sum  += nextScore
avg = total_sum / num_scores

See how that sort of approach works for you

Answer 3

You can just break out of your for loop after getting input.

for n in range(scores):
    c = int(Input('Enter test score, enter 9999 to break'))
    if c == 9999:
       break;
    scores += c

Something like that at least.