用于求数字阶乘的 Python 程序

一个数的阶乘是所有从 1 到该数的整数的乘积。

例如，6 的阶乘是 1*2*3*4*5*6 = 720。负数的阶乘未定义，零的阶乘是一，0! = 1。

使用循环计算一个数的阶乘

# Python program to find the factorial of a number provided by the user.

# change the value for a different result
num = 7

# To take input from the user
#num = int(input("Enter a number: "))

factorial = 1

# check if the number is negative, positive or zero
if num < 0:
   print("Sorry, factorial does not exist for negative numbers")
elif num == 0:
   print("The factorial of 0 is 1")
else:
   for i in range(1,num + 1):
       factorial = factorial*i
   print("The factorial of",num,"is",factorial)

输出

The factorial of 7 is 5040

注意：要测试不同数字的程序，请更改 num 的值。

这里，要计算阶乘的数字存储在 num 中，我们使用 if...elif...else 语句检查数字是负数、零还是正数。如果数字是正数，我们使用 for 循环和 range() 函数计算阶乘。

使用递归计算一个数的阶乘

# Python program to find the factorial of a number provided by the user
# using recursion

def factorial(x):
    """This is a recursive function
    to find the factorial of an integer"""

    if x == 1 or x == 0:
        return 1
    else:
        # recursive call to the function
        return (x * factorial(x-1))


# change the value for a different result
num = 7

# to take input from the user
# num = int(input("Enter a number: "))

# call the factorial function
result = factorial(num)
print("The factorial of", num, "is", result)

在上面的示例中，factorial() 是一个递归函数，它会调用自身。这里，函数将通过递减 x 的值来递归调用自身。

另请阅读

• 使用递归求数字阶乘的 Python 程序