CODEWITHSUNDEEP
pythoniterationaddition
DHowell
DHowell

Reputation: 17

Adding through iteration

I want to take user input and add each number up to 0. For example user inputs 9 I want to add 9+8+7+6.... +1 and output the total. My code

def main(*args):
    sum = 0
    for i in args:
        sum = i + (i - 1)
    return sum

result = main(9)
print(result)

comes close, but I can't get it to iterate through until 0. I've tried adding ranges in a few ways but no luck there. I'm stuck.

Upvotes: 0

Views: 275

Answers (3)

Rich Tier
Rich Tier

Reputation: 9441

Nth triangle number. No iteration needed.

def calculate_nth_triangle_number(value):
    return value * (value + 1) / 2

Upvotes: 2

gboffi
gboffi

Reputation: 25023

Your code misuses a relatively advanced feature of Python, that is argument packing, where all the arguments supplied to a function are packed in a tuple.

What happens when you call main(9)? the loop is entered once (because calling the function with a single argument is equivalent to args = (9, ) in the body of the function) i takes only one value, i = 9 and you have sum = 9+8 = 17.

For your case I don't like a for loop, can you use a while loop? with a while your function follows exactly the definition of your task! 

def my_sum(n):
    result = 0
    while n>0:
        result = result + n
        n = n - 1
    return result

Note that the order of summation and decrease is paramount to a correct result... note also that sum is the name of a built-in function and it is considered bad taste to overload a built-in name with an expression of yours.

Upvotes: 0

rahlf23
rahlf23

Reputation: 9019

Let's say the user input is assigned to x, then the most simplistic answer is:

sum(range(int(x)+1))

Note that range() will generate a list (actually, an immutable sequence type in Python 3) of numbers up to, but not including, x, hence the +1.

In terms of your original code, there are a few issues. First, you should avoid naming variables the same as Python built-ins, such as sum. Second, you are attempting to iterate through a tuple of input arguments (e.g. args = (9,) in your case), which will perform 9 + (9-1), or otherwise 17 and then return that sum as an output.

Instead, you could do something like:

def main(*args):
    mysum = 0
    for i in range(args[0]+1):
        mysum = mysum + i
    return mysum

result = main(9)

print(result)

Both solutions here will return 45.

Upvotes: 2

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