循環到用戶提示

Question

我是一名Python編程的初學者，並且遇到了我的代碼問題。

當用戶鍵入無效操作時，它通知用戶但退出程序（第33行）。我怎樣才能讓用戶再次進入數學運算？

#This python program calculates the sum, difference, product, or quotient of two numbers defined by users. 

#Define add function and return the result of num1 + num2 
def add(num1, num2): 
    return num1 + num2 

#Define subract function and return the result of subtracting num1 - num2 
def sub(num1, num2): 
    return num1 - num2 

#Define multiplication function and return the result of multiplying num1 * num2 
def mul(num1, num2): 
    return num1 * num2 

#Define division function and return the result of dividing num1/num2 
def div(num1, num2): 
    return num1/num2 


#Define main purpose/function of the program 
def main(): 

    #Ask what math operation to perform 
    operation = input("What do you want to do? (+, -, *, /): ") 

    #If the operation is not +, -, *, or /, invalid operation 
    if(operation != '+' and operation != '-' and operation != '*' and operation != '/'): 
     print("You must enter a valid operation!") 

    #If valid, perform specified operation 
    else: 
     var1 = int(input("Enter num1: ")) 
     var2 = int(input("Enter num2: ")) 
     if(operation == '+'): 
      print(add(var1, var2)) 
     elif(operation == '/'): 
      print(div(var1, var2)) 
     elif(operation == '-'): 
      print(sub(var1, var2)) 
     else: 
      print(mul(var1, var2)) 

main() 

Answer 1

只需再次要求用戶輸入它：

#This python program calculates the sum, difference, product, or quotient of two numbers defined by users. 

#Define add function and return the result of num1 + num2 
def add(num1, num2): 
    return num1 + num2 

#Define subract function and return the result of subtracting num1 - num2 
def sub(num1, num2): 
    return num1 - num2 

#Define multiplication function and return the result of multiplying num1 * num2 
def mul(num1, num2): 
    return num1 * num2 

#Define division function and return the result of dividing num1/num2 
def div(num1, num2): 
    return num1/num2 


#Define main purpose/function of the program 
def main(): 

    #Ask what math operation to perform 
    operation = input("What do you want to do? (+, -, *, /): ") 

    #If the operation is not +, -, *, or /, invalid operation 
    while (operation != '+' and operation != '-' and operation != '*' and operation != '/'): 
     print("You must enter a valid operation!") 
     operation = input("What do you want to do? (+, -, *, /): ") 

    var1 = int(input("Enter num1: ")) 
    var2 = int(input("Enter num2: ")) 
    if(operation == '+'): 
     print(add(var1, var2)) 
    elif(operation == '/'): 
     print(div(var1, var2)) 
    elif(operation == '-'): 
     print(sub(var1, var2)) 
    else: 
     print(mul(var1, var2)) 
main() 

Answer 2

如果您使用的是Python2，則不能在此處使用輸入，因爲input（）將評估執行上下文中的輸入。所以，你應該使用raw_input（）。在Python-3.x的情況下，你可以使用input（）。

就你的問題而言，你可以把它放到一個while循環中。

#This python program calculates the sum, difference, product, or quotient of two numbers defined by users. 

#Define add function and return the result of num1 + num2 
def add(num1, num2): 
    return num1 + num2 

#Define subract function and return the result of subtracting num1 - num2 
def sub(num1, num2): 
    return num1 - num2 

#Define multiplication function and return the result of multiplying num1 * num2 
def mul(num1, num2): 
    return num1 * num2 

#Define division function and return the result of dividing num1/num2 
def div(num1, num2): 
    return num1/num2 


#Define main purpose/function of the program 
def main(): 

    while True: 
     #Ask what math operation to perform 
     operation = raw_input("What do you want to do? (+, -, *, /): ") 
     print "operation is ", operation, type(operation) 

     #If the operation is not +, -, *, or /, invalid operation 
     if operation != '+' and operation != '-' and operation != '*' and operation != '/': 
     print("You must enter a valid operation!") 
     #If valid, perform specified operation 
     else: 
     var1 = int(input("Enter num1: ")) 
     var2 = int(input("Enter num2: ")) 
     if(operation == '+'): 
      print(add(var1, var2)) 
     elif(operation == '/'): 
      print(div(var1, var2)) 
     elif(operation == '-'): 
      print(sub(var1, var2)) 
     else: 
      print(mul(var1, var2)) 
     return 0 

main()