Expert: Joseph Moore - 7/27/2009

Question
QUESTION: is only if statement require in recursion?

ANSWER: Recursion occurs when you call the same function repeatedly with slightly differing input values, expecting to reach an end point that will cascade results back to every previous calling of the function.  An easy to understand example of recursion is the factorial operation of numbers.

The factorial of an integer (non-negative) is defined as the product of every positive integer less than or equal to the integer.  The symbol for a factorial is the exclamation point (!).  So, the factorial of A (represented as A!) would be the product of every integer from 1 to A.  5!, for example, is:

   1 * 2 * 3 * 4 * 5 = 120

The algorithm for this is really quite simple and makes for an easy recursive function:

   int factorial(int num)
   {
       if (num == 1)
         return num;
       else
         return factorial(num - 1) * num;
   }

You can see here how the function calls itself, decrementing num by one.  In this manner, there is a change in the input value and a defined end point (num == 1).  Once the end point is reached, the return values cascade back until the initial caller of the recursive function is reached.

If you have any further questions, or if I have raised any new questions for you, please do not hesitate to ask.

---------- FOLLOW-UP ----------

QUESTION: why bubble sort called?also name like insertion sort ,selection sort.

Answer
The sorting algorithm names are (theoretically) descriptive of how they work.

Bubble sort is so called because the items "bubble" to the top in sorted order.

Insertion sort works based on the premise that it's building a new array, inserting elements one at a time.

Selection sort is so called because it continuously selects the smallest unsorted value and moves it to its proper place.