NameError x not defined

[Bruizeh]

Hello, my class just began functions() and defining them but I'm stuck rn.

def greeting():
    print("Hello, welcome to the Calculator App")


def menu():
    decide=input("1 for Addition, 2 for Subtraction, 3 for Multiplication, 4 for Division")

def num():
    num1=input("Enter first value")
    num2=input("Enter second value")

def calc():
    if decide == "1":
        ans = num1 + num2
        print(ans)
    if decide == "2":
        ans2 = num1 - num2
        print(ans2)
    if decide == "3":
        ans3 = num1 * num2
        print(ans3)
    if decide == "4":
        ans4 = num1 / num2
        print(ans4)





greeting()

menu()

num()

calc()

When I run this part of code, it yields a "decide" is not defined. I'm not sure what to do as to fix this. Also, I'm confused as to what the parenthesis next to a function should contain, what could and should be added inside the parenthesis?