编程实现一个简单的计算器，具备加法，减法，乘法，除法，阶乘等运算

好的，以下是 Python 语言的实现示例：

def add(x, y):
    return x + y

def subtract(x, y):
    return x - y

def multiply(x, y):
    return x * y

def divide(x, y):
    if y == 0:
        return "Error: Division by zero is not allowed"
    else:
        return x / y

def factorial(x):
    if x < 0:
        return "Error: Factorial of a negative number is not defined"
    elif x == 0:
        return 1
    else:
        return x * factorial(x-1)

print("Select operation.")
print("1.Add")
print("2.Subtract")
print("3.Multiply")
print("4.Divide")
print("5.Factorial")

while True:
    choice = input("Enter choice (1/2/3/4/5): ")

    if choice in ('1', '2', '3', '4', '5'):
        if choice == '5':
            num = int(input("Enter a non-negative integer: "))
            print(factorial(num))
        else:
            num1 = float(input("Enter first number: "))
            num2 = float(input("Enter second number: "))

            if choice == '1':
                print(num1, "+", num2, "=", add(num1, num2))

            elif choice == '2':
                print(num1, "-", num2, "=", subtract(num1, num2))

            elif choice == '3':
                print(num1, "*", num2, "=", multiply(num1, num2))

            elif choice == '4':
                print(num1, "/", num2, "=", divide(num1, num2))
        break
    else:
        print("Invalid Input")

这个程序会根据用户的选择进行不同的计算操作，使用了函数来实现每种运算，同时还有对除零和负数阶乘的错误处理。