Question

How does a recursion stop? If it keeps calling itself, when does it finally end?

Answer 1

never ends if no break and return condition is set , untill stack overflows,

Answer 2

I couldn't get you, can you make it more clear?

Answer 3

when a function calls itself or another function the address of next line to be executed in memory will be stored on a data structure named stack , cause stack has a limit for saving these , when it call itself without any condition its like a always true condition for a a while , like , while(true) { commands here } , when it exceeds stack limit size for program , then occurs an error , named stackoverflow

Answer 4

why would anyone use a recursion without any condition? Is there any purpose behind it?

Answer 5

consider this example , myFunc() { myFunc(); anotherFunc(); }
as you see , anotherFunc() has no chance to be executed , its just an error . i mean a Fatal error

Answer 6

you have to tell it when to stop - give it a 'base case'. in the following example the base case is when the argument is equal to ''
http://pastebin.com/5GUJ2Aum

Answer 7

so,it keeps on calling until any condition is fulfilled? For this case, until the string is empty(blank)?

Answer 8

And what does s[:-1] mean?

Answer 9

i haven't experience with Python , if that's a python code

Answer 10

this is a forum for a course that uses python to learn C.S.
that is a slice, it is in the Python tutorial and some of the early readings

Answer 11

http://docs.python.org/tutorial/introduction.html#strings

Answer 12

And what does s[:-1] mean?
this will return all of the string 's' from the first character to the final character -1.

s = 'foo'
print s[:-1]
>>>fo

Answer 13

How does a recursion stop? If it keeps calling itself, when does it finally end?

you must put a test in the code so that the recursion is stopped. i.e looop test true, or call a return. otherwise infinite loop.

Answer 14

as Jeffrey says above you do need an exit hatch to stop the recursion. one approach is to put to a condition (e.g. an if statement). The following code calculates the factorial of an integer using recursion. Notice in the case of the code above, the recursion stops when the condition n==1 is true.

Answer 15

forgot to post the code. here it is:


def factorial(n):
if n==1:
return 1
else:
return factorial(n-1)*n

x = int(raw_input("Please enter an integer: "))

print factorial(x)