Programming with C: Recursion

Name: Programming with C: Recursion
Author: Mike McMillan

Learn how to implement recursive functions in your C programs

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Course: On-Demand

Hi, this is Mike McMillan and welcome back to this course on intermediate C programming. In this lesson, I'm going to introduce you to writing recursive functions, and I'm going to demonstrate how to write recursive functions with a example where we compute the factorial of a number. For example, four factorial is equal to four times, three times, two times one and it turns out that the factorial function in mathematical terms can be defined recursively. And I'm not going to go into the deep mathematics but for example, we can write four factorial is equal to and so that would be four times, three times, two times one. And so in that way it's kind of calling itself. So that lends itself to a recursive definition. Let's look at how to do that. We're gonna call our function factorial. So the way a factorial program works is, actually let me show you one more example here. One factorial is equal to one, so that's where we stop. So we'll say one factorial equals one. And so the way we want our program to work is kind of backwards. We're gonna first check to see if we're at one and if we're at one, then we're gonna stop. Otherwise, we're gonna multiply whatever we're wherever we're at times the function again. So think of it like this. If n is four, then we're going to compute four times factorial called with three, and then we're gonna call four times three with factorial for two and then four times three times two with factorial for one. And then we're gonna have four times, three times, two times, one, and then we'll get the answer, which is 24. So the way we write that in code as we write the n-1 is very important, because we've gotta get in down from wherever we started to one if we want the function to return with a final result. So let's give it a try. So we'll say so what we should see is four times three is 12 times two is 24 times one is 24. So that should be the answer that we see. And there it is, 24. Let's talk real quick about how a recursive function works. You always have what's called a base case, and this is where we want the function to stop. And it's normally when n is equal to one. It doesn't have to be, but it frequently is. So when once n is equal to one, then we're gonna return whatever n's value is. Otherwise we're going to keep returning n times the next factorial down. So from four, we're gonna go to three, then to two and then we'll get to one, then we'll stop and then the function ends. We can try it with another number. But I know that five factorial is 120, and that again there's our 120, so it works. So that is how recursive functions are defined in C and I thank you very much for watching.

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Course Description

Recursive functions are useful because many times the solution to a problem lends itself to recursion. However, many beginning programmers have problems with recursion because they have never been exposed to the concept.

Defining a function recursively involves understanding how recursive solutions are built. In these lessons, we’ll discuss how to write recursive functions. A recursive function is a function that calls itself in its definition. We’ll begin by demonstrating recursion through computing factorials. Then we’ll move on to a more complex recursive function—computing a term in the Fibonacci sequence. You’ll learn how to perform a simple process recursively, and conclude by comparing the recursive solution vs. the iterative solution for computing powers of numbers.

What You'll Learn

Define recursion and explain its use in programming
Write recursive functions, understanding how recursive solutions are built
Compute factorials using recursion
Compute terms in the Fibonacci sequence using recursion
Print the contents of an array using recursion
Describe the difference between recursive and iterative solutions for computing powers of numbers

Key Takeaways

A recursive function is a function that calls itself in its definition.
Recursive functions are useful because many problems have solutions that lend themselves naturally to recursion.
The course demonstrates recursion first through computing factorials, then through the more complex example of computing a term in the Fibonacci sequence.
The course compares the recursive solution against the iterative solution for computing powers of numbers.

Frequently Asked Questions

What does this C programming course cover?

It covers how to write recursive functions in C, including defining a function recursively, computing factorials with recursion, computing terms in the Fibonacci sequence, printing the contents of an array recursively, and comparing recursive versus iterative solutions for computing powers of numbers.

Who is this course for?

It is aimed at beginning programmers who have not previously been exposed to the concept of recursion and often have problems with it.

What lessons are included?

The course includes three lessons: Recursion Basics; Defining and Using the Factorial Function; and Defining the Power Function.

What skills will I gain from this course?

You will build skills in C (Programming Language), Modular Programming in C, Programming Concepts, Recursion, Recurrence Relation, and Recursive Descent.

What example does the course use to introduce recursion?

It begins by demonstrating recursion through computing factorials, then moves on to a more complex recursive function for computing a term in the Fibonacci sequence.