習題 29: 如果(if)

下面是你要寫的作業(yè)，這段向你介紹了“if語句”。把這段輸入進去，讓它能正確執(zhí)行。然后我們看看你是否有所收獲。

people = 20
cats = 30
dogs = 15


if people < cats:
    print "Too many cats! The world is doomed!"

if people > cats:
    print "Not many cats! The world is saved!"

if people < dogs:
    print "The world is drooled on!"

if people > dogs:
    print "The world is dry!"


dogs += 5

if people >= dogs:
    print "People are greater than or equal to dogs."

if people <= dogs:
    print "People are less than or equal to dogs."


if people == dogs:
    print "People are dogs."

你應(yīng)該看到的結(jié)果

$ python ex29.py 
Too many cats! The world is doomed!
The world is dry!
People are greater than or equal to dogs.
People are less than or equal to dogs.
People are dogs.
$

加分習題

猜猜“if語句”是什么，它有什么用處。在做下一道習題前，試著用自己的話回答下面的問題:

1. 你認為 if 對于它下一行的代碼做了什么？
2. 為什么 if 語句的下一行需要 4 個空格的縮進？
3. 如果不縮進，會發(fā)生什么事情？
4. 把習題 27 中的其它布爾表達式放到``if語句``中會不會也可以運行呢？試一下。
5. 如果把變量 people, cats, 和 dogs 的初始值改掉，會發(fā)生什么事情？