習(xí)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(jìn)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 equal to dogs.
People are less than equal to dogs.
People are dogs.
$

加分習(xí)題

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

1. 你認(rèn)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(jìn)？
3. 如果不縮進(jìn)，會發(fā)生什么事情？
4. 把習(xí)題 26 中的其它布爾表達(dá)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？