#### Overview of this book

Used in everything from microcontrollers to operating systems, C is a popular programming language among developers because of its flexibility and versatility. This book helps you get hands-on with various tasks, covering the fundamental as well as complex C programming concepts that are essential for making real-life applications. You’ll start with recipes for arrays, strings, user-defined functions, and pre-processing directives. Once you’re familiar with the basic features, you’ll gradually move on to learning pointers, file handling, concurrency, networking, and inter-process communication (IPC). The book then illustrates how to carry out searching and arrange data using different sorting techniques, before demonstrating the implementation of data structures such as stacks and queues. Later, you’ll learn interesting programming features such as using graphics for drawing and animation, and the application of general-purpose utilities. Finally, the book will take you through advanced concepts such as low-level programming, embedded software, IoT, and security in coding, as well as techniques for improving code performance. By the end of this book, you'll have a clear understanding of C programming, and have the skills you need to develop robust apps.
Preface
Creativity with Graphics
Improving the Performance of Your Code
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# Finding the greatest common divisor using recursion

In this recipe, we will use recursive functions to find the greatest common divisor (GCD), also known as the highest common factor) of two or more integers. The GCD is the largest positive integer that divides each of the integers. For example, the GCD of 8 and 12 is 4, and the GCD of 9 and 18 is 9.

# How to do it…

The int gcd(int x, int y) recursive function finds the GCD of two integers, x and y, using the following three rules:

• If y=0, the GCD of x and y is x.
• If x mod y is 0, the GCD of x and y is y.
• Otherwise, the GCD of x and y is gcd(y, (x mod y)).

Follow the given steps to find the GCD of two integers recursively:

1. You will be prompted to enter two...