Python 练习——计算1-2+3-4

# 求1-99的所有数的和
count = 1
s = 0
while count < 100:
    s += count
    count += 1
print(s)

count = 1
s = 0
sign = 1  # 用来标记正负号
while count < 100:
    s += sign * count
    sign = -sign  #每次执行累加后，把标记赋值为相反数
    count += 1
print(s)

is_add = True  # 最开始0+1是加法，所以初值为True
count = 1
s = 0
while count < 100:
    if count != 88:  # 把想要剔除的数拒之门外，让计数器下去默默加1
        if is_add:
            s += count
            is_add = False  # 执行加法后，下一次是减法
        else:
            s -= count
            is_add = True  # 执行减法后，下一次是加法
    count += 1
print(s)

s = 0
count = 1
while count <= 99:
    if count % 2 == 0:
        s -= count
    else:
        s += count
    count += 1
print(s)