Recursion

Basics of recursion

Recursion(the page is calling itself - get it?) is an important programming technique that causes a function to call itself. The approach can be applied to many types of problems, and recursion is one of the central ideas of computer science. A common computer programming tactic is to divide a problem into sub-problems of the same type as the original, solve those sub-problems, and combine the results. This is often referred to as the divide-and-conquer method. Recursion and iteration (looping) are strongly related—a function can return the same results either with recursion or iteration. Usually, a particular computation will lend itself to one technique or the other, and you simply choose the most natural or preferable approach.

Base Case

In the base case, the routine does not call itself. Each recursive algorithm must have a criteria to end the recursion, otherwise it would run indefinitely. This criteria is what causes the base case.

Example

 
static int Recursive(int value, ref int count)
    {
	count++;
	if (value >= 10)
	{
	    // throw new Exception("End");
	    return value;
	}
	return Recursive(value + 1, ref count);
    }

static void Main()
    {
	//
	// Call recursive method with two parameters.
	//
	int count = 0;
	int total = Recursive(5, ref count);
	//
	// Write the result from the method calls and also the call count.
	//
	Console.WriteLine(total);
	Console.WriteLine(count);
    }
}

Output

10 Total value of 10 was added up.
6 Six method calls.