#!/usr/bin/env python
# -*- coding: utf-8 -*-
# @Time    : 2018/5/6 0006 12:06
# @Author  : Anthony.Waa
# @Site    : 
# @File    : 求1-2+3-4+5 ... 99的所有數的和.py
# @Software: PyCharm

# demo1
count = 1
sum = 0

while count < 101:
    if count % 2 == 1:
        sum -= count
    elif count % 2 == 0:
        sum += count
    count += 1
print(sum)


# ========================


# demo2
sum = 0
for count in range(1,101):
    if count % 2 == 1:
        sum -= count
    elif count % 2 == 0:
        sum += count
print(sum)

求1-2+3-4+5 ... 99的所有數的和