Python program freeze without eror

Question

Python freeze without error by a simple program if you enter a number with a comma .

-Example for a number: 3.51

the task: Write a program that names an amount entered as the minimum number of coins making up this amount.

-Code made with Python 3.7.1:

print("please enter one euro amount!")
x=float(input())
a=[]
while x>0:
    if x>=2:
        a.append("2€")
        x=x-2
    elif x>=1:
        a.append("1€")
        x=x-1
    elif x>=0.50:
        a.append("50c")
        x=x-0.50
    elif x>=0.20:
        a.append("20c")
        x=x-0.20
    elif x>=0.10:
        a.append("10c")
        x=x-0.10
    elif x>=0.05:
        a.append("5c")
        x=x-0.05
    elif x>=0.02:
        a.append("2c")
        x=x-0.02
    elif x>=0.01:
        a.append("1c")
        x=x-0.01
print("You need at least",len(a),"coins:",a)

no result python freezed /:

Read https://ericlippert.com/2014/03/05/how-to-debug-small-programs/ for tips on debugging your code. Specifically add `print(x)` in your while loop. — Code-Apprentice, Aug 12 '19 at 16:00
Also check out https://stackoverflow.com/questions/588004/is-floating-point-math-broken for a discussion about floating point math. — Code-Apprentice, Aug 12 '19 at 16:03
@alfasin Or `x = 0.9999999` which is almost certain to happen with the subtractions. — Code-Apprentice, Aug 12 '19 at 16:04
Please change while loop condition to check `while int(x) > 0:` instead of `while x > 0:`. See https://repl.it/repls/HonorableImpressiveLinuxkernel — CodeIt, Aug 12 '19 at 16:05

score 1 · Answer 1 · answered Aug 12 '19 at 16:15

The problem is that at some point the variable x is taking a value smaller than 0.01 and at this point your while loop will run forever because you don't have an "else:" statement to break that loop and with that value the code will never enter into any of the "elif ... :" statement you wrote. This is your same code but with an "else" at the end of the loop (assuming that a value that is less than 0.01 is irrelevant to your problem), try it:

print("please enter one euro amount!")
x=float(input())
a=[]
while x>0:
    print(x)
    if x>=2:
        a.append("2€")
        x=x-2
    elif x>=1:
        a.append("1€")
        x=x-1
    elif x>=0.50:
        a.append("50c")
        x=x-0.50
    elif x>=0.20:
        a.append("20c")
        x=x-0.20
    elif x>=0.10:
        a.append("10c")
        x=x-0.10
    elif x>=0.05:
        a.append("5c")
        x=x-0.05
    elif x>=0.02:
        a.append("2c")
        x=x-0.02
    elif x>=0.01:
        a.append("1c")
        x=x-0.01
    else:
        break

print("You need at least",len(a),"coins:",a)

score 0 · Answer 2 · answered Aug 12 '19 at 16:37

Binary floating point numbers can't represent 0.1 so using floating point numbers can have unexpected results. When you subtract 2.0 the result isn't 1.51 as you would expect.

>>> 3.51 - 2.0
1.5099999999999998

The best thing to do is to multiply the users input by 100 and then do integer math (rounding the original result to ensure it is an integer).

Python program freeze without eror

2 Answers2