货币转换器问题

Question

我试图制作货币转换器，但是当我选择选项2或3时，“while”循环不起作用。选择选项1是好的，但另外两个是坏的。

##### Welcome Menu###### 
print("*************************************") 
print("* Queensmead currency converter *")     
print("* 1) Convert from Pound to Dollar *") 
print("* 2) Conver from Dollar to Pound *") 
print("* 3) Quit       *") 
print("*         *") 
print("*************************************") 

print ("Hello, Welcome to the Currency Converter. \nWhat is your name ? ") 
name = input() 

userChoice= input ("Hi " + name + ", Please choose one of the above options ") 

while userChoice == "1": 
    #Prompt the user the amount of Pound they want to convert 
    #Store what the user typed into a vairable 
    userGBP = int(input ("Enter the amount in Pound Stirling you wish to convert to US Dollars: ")) 

    dollar = userGBP * 1.55 
    #Returns the amount to user request 
    print ("£",userGBP , "=", dollar ,"US Dollars") 
    userChoice = input("If you like to convert some more money,please choose from the above Options ") 
    print (userChoice) 



    if userChoice =="2": 
    #Prompt the user the amount of Pound they want to convert 
    #Store what the user typed into a variable 
     userDollar = int(input ("Enter the amount in Dollars you wish to convert to Pound Stirling: ")) 

     pound = userDollar * 0.64 
     #Returns the amount to user request 
     print ("$",userDollar , "=", pound ,"Pound Stirling") 
     userChoice = input("If you like to convert some more money,please choose from the above Options ") 
     print (userChoice) 

    elif userChoice =="3": 
     userQuit = input ("") 
     print ("Thank you for using this program") 

    else: 
    print ("Error: You have entered invalid selection. Please try again") 

Answer 1

替换此：

while userChoice == "1": 

到：

while True: 

是否应该是这样的：

while True: 
    #user input choice 
    if use_choice == 1: 
     #do_stuff 
    if use_choice == 2: 
     #do_stuff 
    if use_choice == 3: 
     break 
    ..... 

Answer 2

你while循环具有条件userChoice == "1";换句话说，当用户选择了第一个选择时，继续运行程序，退出第二个或第三个选择。相反，您可能希望它继续运行您的程序，直到已选择退出。要做到这一点，您需要用userChoice != "3"替换条件。

Answer 3

你的代码有一些缺陷，主要是因为用户选择链接到该while循环，而是应该被链接到一个IF/ELIF/else条件树：

此外，你的代码重演了很多，这是一个不好的做法

print("*************************************") 
print("* Queensmead currency converter *") 
print("*************************************") 

name = input("Hello, Welcome to the Currency Converter. \n" 
       "What is your name? ") 

main_menu = """ 
************************************* 
* 1) Convert from Pound to Dollar * 
* 2) Conver from Dollar to Pound * 
* 3) Quit       * 
*************************************""" 
print(main_menu) 
userChoice = input("Hi " + name + ", Please choose one of the above options: ") 


def convert_to(value, ratio): 
    return value * ratio 


while True: 
    if userChoice == "1": 
     currency_from = "Pound Stirling" 
     currency_to = "US Dolar" 
     ratio = 1.55 
    elif userChoice == "2": 
     currency_to = "Pound Stirling" 
     currency_from = "US Dolar" 
     ratio = 0.64 
    elif userChoice == "3": 
     print ("Thank you for using this program") 
     userQuit = input("") 
     break 
    else: 
     print ("Error: You have entered invalid selection. Please try again") 
    try: 
     value = int(input("Enter the amount in %s you wish to convert to %s: " % (currency_from, currency_to))) 
     converted_value = convert_to(value, ratio) 
     print ("%0.2f %s = %0.2f %s" % (value, currency_from, converted_value, currency_to)) 
    except NameError: 
     pass 
    input("Press ENTER to continue") 
    print main_menu 
    userChoice = input("If you like to convert some more money,please choose from the above Options: ") 

这里有一个代码审查：

1. 改变主菜单的顺序，以显示 选项的用户名拍摄后。
2. 使main_menu成为一个变量，所以它可以在 转换后重复使用。
3. 创建一个处理转换的函数，只留下 循环来设置。
4. 循环获取userChoice，并根据它设置货币来源，currency_to和它们之间的比率。在userChoice'3'上设置的中断为 以离开循环。
5. 变量'value'，取用户输入，格式为 字符串格式化（％符号），需要currency_to和 currency_from。
6. converted_value发送'value'和'ratio'，并捕获 新值
7. 转换后的值将再次使用字符串格式化显示。
8. 主菜单再次
9. 的试印刷/除位是在情况下，用户在 进入无效的选项菜单，它会引发NameError因为currency_from， currency_to和比率将不存在。