Why doesn't the function in my while loop use the updated variable value

Question

So I'm taking a beginner Python class and one of my questions is to write code that takes n number (e.g. 5) and asks the user to enter n-1 numbers in n and finds the missing number. I can't use anything more advanced than loops.

For some reason even though the value of nn gets updated ever time the loop runs the value of number only decreases by 1 every time the loop runs.

n = int(input('Please enter n: '))
ntotal = int(n*(n+1)/2)
print ('Please enter n: ')

print (ntotal)
i = 0
k = i
while i != n-1:
    nn = int(input('Please enter a number: '))
    number = ntotal - nn
    print (nn)
    i += 1

print (number)

You assign to "number" in each loop iteration but you only use last value. — Michael Butscher
– Michael Butscher, Commented Dec 15, 2019 at 2:18
you should use ntotal = ntotal - nn and at the end use print(ntotal) — furas
– furas, Commented Dec 15, 2019 at 2:19
Your code seems to do more than what you described and it's confusing. What is ntotal supposed to be? Why print('Please enter n: ')? Also k is unused. Please make a minimal reproducible example. — wjandrea
– wjandrea, Commented Dec 15, 2019 at 2:22
Also are you not allowed to use range? BTW welcome to Stack Overflow! Check out the tour. — wjandrea
– wjandrea, Commented Dec 15, 2019 at 2:24

furas · Accepted Answer · 2019-12-15 02:24:40Z

1

You have to change ntotal

    ntotal = total - number

or shorter

    ntotal -= number

and display ntotal at the end

n = int(input('Please enter n: '))
ntotal = int(n*(n+1)/2)

#print('ntotal:', ntotal)

i = 0
while i != n-1:
#for _ in range(n-1):
    number = int(input('Please enter a number: '))
    ntotal -= number
    #print('number:', number, 'ntotal:', ntotal)
    i += 1

print(ntotal)

answered Dec 15, 2019 at 2:24

furas

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