How to program the following on python

Question

How to compute the sum 1-2+3-4+.....+1999-2000
I tried
n<=2000
for i in range(1,2001):
print(n-i)
But i dont get it how to even change the sign every time 1 number adds

Answer 1

Elliot, you have not been far away from a good solution with your code, some typos, that result in problems.

Here is your slightly reworked code:

sum_ = 0
for i in range(1,2001):
if i%2==0:
sum_ = sum_ - i
else:
sum_ = sum_ + i
print(sum_)

Answer 2

First assign sum=0..now,
As you can see negative sign comes when the no. Is divisible by 2... So you can make condition that if i%2==0 then do sum=sum-i else sum=sum+i

then print sum ...

I hope it helps..🙃

Answer 3

Thank you all

Answer 4

Ok
I still not get it why it doesn't work but I tried
Sum=0
for I in range(1,2001):
if i%2==0:
sum=sum+1
else:
sum=sun-I
Print(sum)
But it prints 0

Answer 5

sum(range(1, 2001, 2)) - sum(range(2, 2001, 2))