can someone explain why the second code works but not the first?-CodePudding

given_list = [7,5,4,4,3,1,-2,-3,-5,-7]
total1 = 0
i = 0
while given_list[i] < 0 and i < len(given_list):
    total1  = given_list[i]
    i  = 1
print(total1)

I am trying to add all the negative numbers together. The code above gives the answer 0.The code below gives the answer -17 (the correct answer). Why do they give different answers? To me it looks like both of them are the same, just written differently. I am clearly misunderstanding something. Can someone help me wrap my head around this?

given_list = [7,5,4,4,3,1,-2,-3,-5,-7]
total1 = 0
i = 0
while i < len(given_list):
    if given_list[i] < 0:
        total1  = given_list[i]
    i  = 1
print(total1)

CodePudding user response：

It's because the while loop first condition (while given_list[i] < 0) is false for the first element itself (7) and the loop doesn't execute itself. You can try printing the current looped element for more clarity

given_list = [7,5,4,4,3,1,-2,-3,-5,-7]
total1 = 0
i = 0
while given_list[i] < 0 and i < len(given_list):
    total1  = given_list[i]
    print(given_list[i])
    i = i   1
print(total1)

You can also try the above code minus the given_list[i] < 0 and print each looped item.

CodePudding user response：

The first while breaks at the first element of the list, because the condition evaluates to false. This happens because given_list[i] < 0 at Index 0, the value is greater than 0.

CodePudding user response：

It's because of the given_list[i] < 0. Your array will not pass this condition and not enter the loop. This will only pass if you negative numbers are first and then the others.

CodePudding user response：

The first program doesn't work because a while loop breaks when it's condition is false. So as soon as the loop enounters a positive number in the list, given_list[i] < 0 becomes false and the loop breaks.

What you want is to go through the whole list and check each element whether it is positive or not without breaking the loop.