Python -- Confusing result when combining for loop with while loop-CodePudding

Hi I'm new to programming. I tried to use for loop and a nested while loop to calculate the sum of an arithmetic sequence on condition that the sum is no bigger than 100. I wrote the code below, but the output was 100 instead of the correct sum of the elements of the sequence (which should be 92).

# Arithmetic sequence
ele = 1
diff = 3
arithmetic_sequence = []
while ele < 60:
    arithmetic_sequence.append(ele)
    ele  = diff

print(arithmetic_sequence)

#[output: [1, 4, 7, 10, 13, 16, 19, 22, 25, 28, 31, 34, 37, 40, 43, 46, 49, 52, 55, 58]]

# Sum of the arithmetic sequence -- the output is 100, very weird
sum_arithmetic = 0
for ele_f in arithmetic_sequence:
    while sum_arithmetic < 100:
        sum_arithmetic  = ele_f

print(sum_arithmetic)

#[output: 100]

Could anyone help me check what went wrong in my code? Thank you in advance!

CodePudding user response：

You need not use a while loop inside the for, your code as of now keeps adding the same ele_f until it reaches a sum less than 100, so basically it is adding 1 100 times which gives 100, after which the condition is no longer true for any other ele_f in arithmetic_sequence.

In other words, your for loop executes the while part only for the first element.

You need this (if instead of while and the condition is changed slightly)

sum_arithmetic = 0
for ele_f in arithmetic_sequence:
    if (sum_arithmetic   ele_f) < 100:
        sum_arithmetic  = ele_f

CodePudding user response：

Putting a nested while loop in the for loop is not doing that you think it is.

What you want to do is:

Loop over the elements of the sequence, adding the current element at each iteration
If the sum is greater than or equal to 100, stop there and keep the sum under 100

However what you are actually doing is:

Looping over all the elements of the sequence
At each iteration, adding the current element until the sum is 100

So all your code does is repeatedly add 1, and never add any of the other elements. (Because the sum is already 100, from all the 1s that you added.)

What you want is an if statement inside the for loop to check if it should continue:

sum_arithmetic = 0
for ele_f in arithmetic_sequence:
    if sum_arithmetic   ele_f >= 100:
        break
    sum_arithmetic  = ele_f

In this code, the break will end the for loop early if the if statement ever runs.