Creating a loop to check a variable to make sure it is a positive integer

Question

I'm trying to create a program that creates a list of the first nth Fibonacci terms. The program itself works in that it creates the list of Fibonacci numbers. The problem is that I want to make it check to make sure that n is a positive integer but I do not know how.

Here's the code:

n = int(input("Please enter the number of Fibonacci numbers you want: "))
def fib(n):
    if 0 <= n <= 1:
        return 1
    else:
        return(fib(n-1) + fib(n-2))

if n < 0:
   print("Please enter a positive integer")
   n = None
   fib(n)
else:
   for i in range(n):
       print(fib(i), end=", ")       

ender = input("\nPress enter to end the program\n")

• To start, it askes for a user input of n, which is set to be an integer
• Then program defines the function fib(n)
• Then it checks if n is equal to 1 or 0 and returns the value 1
• If not, then it does the Fibonacci sequence on the value n
• Then a check is done, if n < 0 then print the error and remove the value of n
• This is where the problem arises in that it cannot loop back and replace the value of n since it would create an infinite loop, and I can't define the integer value of n inside the fib(n) function
• The else statement is just formatting and prints out the Fibonacci numbers in a list separated by commas and spaces, and ender holds the program so that it doesn't end automatically.

How would I go about creating a loop that removes the negative value of n and asks for it again?

Many Thanks

Answer 1

设置n为-1，然后有一个循环，询问新n只要当前值n为负。

Answer 2

To expand a bit on what the others have given you:

n = -1
while n < 0:
    try:
        n = int(input("Please enter the number of Fibonacci numbers you want: "))
    except ValueError:
        continue

Which will handle users who try to sneakily put in values like HELLO instead of 5

Answer 3

A good way to go about this is the following:

n = int(input("Please enter the number of Fibonacci numbers you want: "))

while n < 0:

    n = int(input("Bad input! try again: "))

*** do your other things ***

This way, it repeatedly checks until you have good input.

Answer 4

You can set up a while loop in the beginning of your code:

n = -1
while n <= 0:
    n = int(input("Please enter the number of Fibonacci numbers you want: "))

Answer 5

You can use a boolean variable, you keep looping until you enter a positive number, in this case you turn the value to be False

def fib(n):
    if 0 == n and n == 1:
        return 1
    else:
        return(fib(n-1) + fib(n-2))
isTrue= True

while isTrue: 
    n = int(input("Please enter the number of Fibonacci numbers you want: "))

    if n < 0:
        print("Please enter a positive integer")
    else:
        isTrue= False
        for i in range(n):
            print(fib(i), end=", ")       

ender = input("\nPress enter to end the program\n")