使用 Linkbot 學習 Python 3 / 計數到 10

課程資訊

**To Be Added**
Vocabulary:
Necessary Materials and Resources:
Computer Science Teachers Association Standards: 5.2.CPP.5: Implement problem solutions using a programming 
language, including: looping behavior, conditional statements, logic, expressions, variables, and functions.
Common Core Math Content Standards:
Common Core Math Practice Standards:
Common Core English Language Arts Standards:

While 迴圈

通常情況下，計算機從第一行開始，然後向下執行。控制結構改變語句的執行順序或決定是否執行某個語句。以下是一個使用 while 控制結構的程式的原始碼

a = 0 # FIRST, set the initial value of the variable a to 0(zero).
while a < 10: # While the value of the variable a is less than 10 do the following:
    a = a + 1    # Increase the value of the variable a by 1, as in: a = a + 1! 
    print(a)     # Print to screen what the present value of the variable a is.
                 # REPEAT! until the value of the variable a is equal to 9!? See note. 
                 
                 # NOTE:
                 # The value of the variable a will increase by 1
                 # with each repeat, or loop of the 'while statement BLOCK'.
                 # e.g. a = 1 then a = 2 then a = 3 etc. until a = 9 then...
                 # the code will finish adding 1 to a (now a = 10), printing the 
                 # result, and then exiting the 'while statement BLOCK'. 
                 #              --
                 # While a < 10: |
                 #     a = a + 1 |<--[ The while statement BLOCK ]
                 #     print (a) |
                 #              --

以下是極其令人興奮的輸出

（你以為把你的計算機變成一個五美元的計算器後，情況就不可能變得更糟了嗎？）

那麼這個程式做了什麼？首先，它看到 a = 0 這行程式碼，並將 a 設定為零。然後它看到 while a < 10:，因此計算機檢查 a < 10 是否為真。計算機第一次看到這個語句時，a 為零，所以它小於 10。換句話說，只要 a 小於十，計算機就會執行縮排的語句。這最終會使 a 等於十（透過不斷地給 a 加一），然後 while a < 10 就不再為真了。到達那個點後，程式將停止執行縮排的行。

請務必在 while 語句行的末尾新增一個冒號“:”！

以下是另一個使用 while 的例子

a = 1
s = 0
print('Enter Numbers to add to the sum.')
print('Enter 0 to quit.')
while a != 0:
    print('Current Sum:', s)            
    a = float(input('Number? '))        
    s = s + a                            
print('Total Sum =', s)

Enter Numbers to add to the sum.
Enter 0 to quit.
Current Sum: 0
Number? 200
Current Sum: 200.0
Number? -15.25
Current Sum: 184.75
Number? -151.85
Current Sum: 32.9
Number? 10.00
Current Sum: 42.9
Number? 0
Total Sum = 42.9

請注意，print 'Total Sum =', s 只在最後執行。while 語句隻影響縮排的程式碼行。!= 表示不等於，所以 while a != 0: 表示只要 a 不為零，就執行其後的縮排語句。

請注意，a 是一個浮點數，並不是所有浮點數都能被精確地表示，因此對它們使用 != 有時可能無法正常工作。嘗試在互動模式下輸入 1.1。

無限迴圈或永無止境的迴圈

現在我們有了 while 迴圈，就可以讓程式永遠執行。一個簡單的方法是編寫一個像這樣的程式

while 1 == 1:
   print("Help, I'm stuck in a loop.")

“==” 運算子用於測試運算子兩側表示式的相等性，就像之前使用的 “<” 用於“小於”一樣（你將在下一章中獲得所有比較運算子的完整列表）。

這個程式將輸出 Help, I'm stuck in a loop. 直到宇宙熱寂或你停止它，因為 1 將永遠等於 1。停止它的方法是同時按下 Control（或 Ctrl）鍵和 C（字母）。這將殺死程式。（注意：有時你需要在按下 Control-C 後再按回車鍵。）在某些系統上，除了殺死程序之外，沒有任何方法可以阻止它，所以請避免使用它！

示例

斐波那契數列

Fibonacci-method1.py

# This program calculates the Fibonacci sequence
a = 0
b = 1
count = 0
max_count = 20

while count < max_count:
    count = count + 1
    print(a, end=" ")  # Notice the magic end=" " in the print function arguments  
                       # that keeps it from creating a new line.
    old_a = a    # we need to keep track of a since we change it.
    a = b
    b = old_a + b
print() # gets a new (empty) line.

輸出

0 1 1 2 3 5 8 13 21 34 55 89 144 233 377 610 987 1597 2584 4181

請注意，由於 print 引數中添加了額外的引數 end=" "，輸出在單行上。

Fibonacci-method2.py

# Simplified and faster method to calculate the Fibonacci sequence
a = 0
b = 1
count = 0
max_count = 10

while count < max_count:
    count = count + 1
    print(a, b, end=" ")  # Notice the magic end=" "
    a = a + b    
    b = a + b
print() # gets a new (empty) line.

輸出

0 1 1 2 3 5 8 13 21 34 55 89 144 233 377 610 987 1597 2584 4181

輸入密碼

Password.py

# Waits until a password has been entered. Use Control-C to break out without
# the password

#Note that this must not be the password so that the
# while loop runs at least once.
password = str()

# note that != means not equal
while password != "unicorn":
    password = input("Password: ")
print("Welcome in")

示例執行

Password: auo
Password: y22
Password: password
Password: open sesame
Password: unicorn
Welcome in

Linkbot 音樂示例

Linkbot 具有一個小的蜂鳴器，可以一次播放一個音符。我們可以控制 Linkbot 上蜂鳴器的頻率來生成不同的音調。公式 $\mathrm {pianokeyFrequency} =2^{((\mathrm {key} -49)/12)}*440$ 顯示瞭如何計算鋼琴琴鍵的頻率。真正的鋼琴有 88 個琴鍵，但讓我們看看我們是否可以讓我們的機器人從第 34 個琴鍵一直演奏到第 73 個琴鍵。

在 Python 中，要計算一個數字的“次方”，我們可以使用 ** 運算子。例如， $2^{3}$ 可以使用 Python 中的 2**3 來計算。

import barobo
dongle = barobo.Dongle()
dongle.connect()
robotID = input('Enter Linkbot ID: ')
robot = dongle.getLinkbot(robotID)
import time # imports the Python "time" module because we want to use "time.sleep()" later.
key=34 # Set key=34 which is the 34th key on a piano keyboard.
while key < 74: # While the key number is less than 74.
    robot.setBuzzerFrequency(2**((key-49)/12.0)*440)  # Play the frequency to the corresponding note.
    time.sleep(.25)   # Play the note for 0.25 seconds.
    robot.setBuzzerFrequency(0)  # Turn off the note
    key=key+1         # Increase the key number by 1. This is the end of the loop. At this point,
                      # Python will check to see if the condition in the "while" statement,
                      # "key < 74", is true. If it is still true, Python will go back to the 
                      # beginning of the loop. If not, the program exits the loop.

練習

編寫一個程式，要求使用者輸入登入名和密碼。然後，當他們輸入“lock”時，需要輸入他們的使用者名稱和密碼來解鎖程式。

解決方案

編寫一個程式，要求使用者輸入登入名和密碼。然後，當他們輸入“lock”時，需要輸入他們的使用者名稱和密碼來解鎖程式。

name = input("What is your UserName: ")
password = input("What is your Password: ")
print("To lock your computer type lock.")
command = None
input1 = None
input2 = None
while command != "lock":
    command = input("What is your command: ")
while input1 != name:
    input1 = input("What is your username: ")
while input2 != password:
    input2 = input("What is your password: ")
print("Welcome back to your system!")

如果你希望程式連續執行，只需在整個程式周圍新增一個 while 1 == 1: 迴圈。在程式碼頂部新增此迴圈時，你需要縮排程式的其餘部分，但不用擔心，你不需要手動對每一行進行縮排！只需選中你想要縮排的所有內容，然後單擊 python 視窗頂部的“格式”下的“縮排”。

另一種方法是

name = input('Set name: ')
password = input('Set password: ')
while 1 == 1:
    nameguess=""
    passwordguess=""
    key=""
    while (nameguess != name) or (passwordguess != password):
        nameguess = input('Name? ')
        passwordguess = input('Password? ')
    print("Welcome,", name, ". Type lock to lock.")
    while key != "lock":
        key = input("")

請注意 while (nameguess != name) or (passwordguess != password) 中的 or，我們還沒有介紹它。你可能已經猜到它的工作原理了。

修改 Linkbot 蜂鳴器程式，使其演奏從第 34 個琴鍵到第 74 個琴鍵的鋼琴上每隔三個琴鍵的音調。

解決方案

import barobo
dongle = barobo.Dongle()
dongle.connect()
robotID = input('Enter Linkbot ID: ')
robot = dongle.getLinkbot(robotID) 
import time       # imports the Python "time" module because we want to use "time.sleep()" later.
key=34            # Set key=34 which is the 34th key on a piano keyboard.
while key < 74:   # While the key number is less than 74.
    robot.setBuzzerFrequency(2**((key-49)/12.0)*440)  # Play the frequency to the corresponding note.
    time.sleep(.25)   # Play the note for 0.25 seconds.
    robot.setBuzzerFrequency(0)  # Turn off the note
    key=key+3         # Increase the key number by 3. This is the end of the loop. At this point,
                      # Python will check to see if the condition in the "while" statement,
                      # "key < 74", is true. If it is still true, Python will go back to the 
                      # beginning of the loop. If not, the program exits the loop.

使用 Linkbot 學習 Python 3
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