作业01：求1-2+3-4+5...99的所有数的和
sum = 0
count = 1
while count < 100:
if count % 2 == 0:
sum = sum - count
else:
sum = sum + count
count += 1
print(sum)
sum = 0
count = 1
while count < 100:
if count % 2 == 0:
sum = sum - count
else:
sum = sum + count
count += 1
print(sum)