Python while loop subtraction

Question

這是一個非常愚蠢的問題，但我沒有在一段時間內使用過它，並且不記得如何去做。我正在做一個遞歸問題，並需要顯示數字倒數基本顯示遞歸如何工作。但是，我似乎無法弄清楚。這是我的代碼。

def main(): 

    #have user input first number 
    x = int(input('Enter the first number: ')) 

    #have user input second number 
    y = int(input('Enter the second number: ')) 

    #calculate result by calling recursive function 
    result = mult(x, y) 

    #print the result 
    print(x, 'times', y, 'is', result) 

#define a function that uses recursion 
def mult(x, y): 
    # create a loop to display the numbers 
    count = y 
    while count > 0: 
     print('First number =', x, 'Second number =', count) 
     count -= 1 
    #use recursion to multiply the numbers 
    if x == 0: 
     return 0 
    elif x == 1: 
     return y 
    else: 
     return y + mult(x - 1, y) 

main() 

我需要的輸出這樣說：

Enter the first number: 5 
Enter the second number: 7 
First number = 5 Second Number = 7 
First number = 5 Second Number = 6 
First number = 5 Second Number = 5 
First number = 5 Second Number = 4 
First number = 5 Second Number = 3 
First number = 5 Second Number = 2 
First number = 5 Second Number = 1 
5 times 7 = 35 

所以它的工作大部分，但現在它顯示的是這樣的：

Enter the first number: 5 
Enter the second number: 7 
First number = 5 Second number = 7 
First number = 5 Second number = 6 
First number = 5 Second number = 5 
First number = 5 Second number = 4 
First number = 5 Second number = 3 
First number = 5 Second number = 2 
First number = 5 Second number = 1 
First number = 4 Second number = 7 
First number = 4 Second number = 6 
First number = 4 Second number = 5 
First number = 4 Second number = 4 
First number = 4 Second number = 3 
First number = 4 Second number = 2 
First number = 4 Second number = 1 
First number = 3 Second number = 7 
First number = 3 Second number = 6 
First number = 3 Second number = 5 
First number = 3 Second number = 4 
First number = 3 Second number = 3 
First number = 3 Second number = 2 
First number = 3 Second number = 1 
First number = 2 Second number = 7 
First number = 2 Second number = 6 
First number = 2 Second number = 5 
First number = 2 Second number = 4 
First number = 2 Second number = 3 
First number = 2 Second number = 2 
First number = 2 Second number = 1 
First number = 1 Second number = 7 
First number = 1 Second number = 6 
First number = 1 Second number = 5 
First number = 1 Second number = 4 
First number = 1 Second number = 3 
First number = 1 Second number = 2 
First number = 1 Second number = 1 
5 times 7 is 35 

Answer 1

它看起來像你對我沒有存儲您修改的y值。因此，while循環應該這樣寫：

y_temp = y 
while y_temp > 0: 
    print('First number =', x, 'Second number =', y_temp) 
    y_temp -= 1 

Answer 2

你忘了更新y，你沒有減少y。

Answer 3

只需進行一些小的更改即可，您需要更新while loop中的y的值。

#create a loop to display the numbers 
while y > 0: 
    print('First number =', x, 'Second number =', y) 
    y -= 1 

Answer 4

你while循環是遞歸調用之外，所以y值不會得到更新。將print語句移入mult函數中，並在if語句之上。

def mult(x, y): 
    print('First number =', x, 'Second number =', y) 
    print('First number =', x, 'Second number =', y - 1) 
    if x == 0: 
     return 0 
    elif x == 1: 
     return y 
    else: 
     return y + mult(x - 1, y) 

Answer 5

打印這兩個數字的目的是跟蹤遞歸。所以很自然地，這些數字必須從內部的遞歸函數中打印出來。換句話說，你不想創建一個額外的循環（使用while）來顯示數字，但遞歸是循環。

你也只想打印一次每個遞歸步驟。

什麼可能另外混淆的是你已交換的「第一」/x和「第二」/y所需的輸出和遞歸的參數順序之間的角色。 （您想在「第二」號在輸出減少，但你減少mult的第一參數（x）。）

它應該是這樣的：

def mult(x, y): 
    """Calculate x * y by using recursion.""" 
    print('First number =', x, 'Second number =', y) 
    if y == 0: 
     return 0 
    elif y == 1: 
     return x 
    else: 
     return x + mult(x, y - 1) 

if __name__ == '__main__': 
    x = int(input('Enter the first number: ')) 
    y = int(input('Enter the second number: ')) 

    # calculate result by calling recursive function 
    result = mult(x, y) 

    # print the result 
    print(x, 'times', y, 'is', result)