一、if語句

格式：

i1 = 3
if i1 > 4:
    print(‘yes you are right‘)
elif 0 < i1 < 4:
    print(‘im dont konw‘)
else:
    print(‘no you are wrong‘)

註意if、elif以及else後面的（:）符號，我們通過它告訴Python下面跟著一個語句塊。

二、while語句

number = 23
running = True

while running:
    guess = int(input(‘enter an integer:‘))

    if guess == number:
        print(‘congratulations,you guessed it‘)
        running = False
    elif guess < number:
        print(‘no,it is a little lower than that‘)
    else:
        print(‘no,it is a little higher than that ‘)
else:
    print(‘the while loop is over‘)

print(‘done‘)

輸出結果：

enter an integer:22
no,it is a little lower than that
enter an integer:24
no,it is a little higher than that
enter an integer:23
congratulations,you guessed it
the while loop is over
done

註意：在Python2.x版本中輸入使用的是raw_input而在Python3.x版本中輸入使用的是input。並且後面都要跟冒號。

三、for循環

格式：for...in

for i in range(1,5):
    print(i)
else:
    print(‘the loop is over‘)

結果：
C:\Python36\python.exe C:/Users/蔡瑞/7.py
1
2
3
4
the loop is over

Process finished with exit code 0

註意：range(1,5)只是輸出1-4沒有5。還有，else部分是可選的，如果包含else，它總是在for循環結束後執行一次，除非遇到break語句。

for循環在這個範圍內遞歸，這就相當於把序列中的每個數（或對象）賦值給i，一次一個，然後以每個i的值執行這個程序塊。

Programming is fun

When the work is done

if you wanna make your work also fun:

　　use Python

Python之‘’控制流‘’