What is recursion and when should I use it?

Answer 1

Recursion is the process where a method call iself to be able to perform a certain task. It reduces redundency of code. Most recurssive functions or methods must have a condifiton to break the recussive call i.e. stop it from calling itself if a condition is met - this prevents the creating of an infinite loop. Not all functions are suited to be used recursively.

Answer 2

Recursion works best with what I like to call "fractal problems", where you're dealing with a big thing that's made of smaller versions of that big thing, each of which is an even smaller version of the big thing, and so on. If you ever have to traverse or search through something like a tree or nested identical structures, you've got a problem that might be a good candidate for recursion.

People avoid recursion for a number of reasons:

1. Most people (myself included) cut their programming teeth on procedural or object-oriented programming as opposed to functional programming. To such people, the iterative approach (typically using loops) feels more natural.

2. Those of us who cut our programming teeth on procedural or object-oriented programming have often been told to avoid recursion because it's error prone.

3. We're often told that recursion is slow. Calling and returning from a routine repeatedly involves a lot of stack pushing and popping, which is slower than looping. I think some languages handle this better than others, and those languages are most likely not those where the dominant paradigm is procedural or object-oriented.

4. For at least a couple of programming languages I've used, I remember hearing recommendations not to use recursion if it gets beyond a certain depth because its stack isn't that deep.

Answer 3

Recursion as it applies to programming is basically calling a function from inside its own definition (inside itself), with different parameters so as to accomplish a task.

Answer 4

You want to use it anytime you have a tree structure. It is very useful in reading XML.

Answer 5

In plain English: Assume you can do 3 things:

1. Take one apple
2. Write down tally marks
3. Count tally marks

You have a lot of apples in front of you on a table and you want to know how many apples there are.

start
  Is the table empty?
  yes: Count the tally marks and cheer like it's your birthday!
  no:  Take 1 apple and put it aside
       Write down a tally mark
       goto start

The process of repeating the same thing till you are done is called recursion.

I hope this is the "plain english" answer you are looking for!

Answer 6

In plain English, recursion means to repeat someting again and again.

In programming one example is of calling the function within itself .

Look on the following example of calculating factorial of a number:

public int fact(int n)
{
    if (n==0) return 1;
    else return n*fact(n-1)
}