Introduction to C Programming

 Introduction to C Programming

C is one of the oldest, most well-known, and influential programming languages. It is widely used across various industries due to its flexibility and power.

Learning C is a valuable endeavor for anyone, regardless of your starting point or goals, as it lays a solid foundation for your entire programming career. It helps you understand the inner workings of a computer, such as how information is stored and retrieved, and provides insights into the internal architecture.

However, C can be challenging to learn, especially for beginners, as it can be cryptic.

This handbook aims to teach you the fundamentals of C programming and is designed with the beginner in mind. There are no prerequisites, and no prior knowledge of programming concepts is required.

If you have never programmed before and are a complete beginner, you are in the right place.

Chapter 1: Introduction to C Programming

Overview

In this introductory chapter, you’ll explore the key characteristics and applications of the C programming language. You will also delve into the fundamentals of C syntax and become acquainted with the general structure of C programs.

By the end of this chapter, you will have set up a development environment for C programming on your local machine, enabling you to follow along with the coding examples in this book. You will have written, compiled, and executed your first simple C program that prints “Hello, world!” to the screen. Additionally, you’ll learn some core features of the C language, such as using comments to document and explain your code and employing escape sequences to represent non-printable characters in text.

What Is Programming?

Computers, despite their speed and data-processing capabilities, cannot think for themselves. They require explicit, detailed instructions to perform tasks. These instructions, collectively known as a program, tell the computer exactly what to do step by step.

Programming is the process of writing these instructions in a form that a computer can understand and execute to accomplish specific tasks and solve particular problems. The instructions are written using a programming language, and the individuals who create these instructions are called programmers.

Types of Programming Languages: Low-level, High-level, and Middle-level

Programming languages can be classified into three categories: low-level, high-level, and middle-level languages.

Low-level Languages

Low-level languages include machine language and assembly language, which provide minimal abstraction from a computer’s hardware. Their instructions closely correspond to specific machine instructions, allowing for speed, efficiency, minimal memory consumption, and detailed control over hardware.

• Machine Language: The lowest level of programming languages, consisting of binary code (0s and 1s) directly executed by the computer’s processor. While efficient, it is not human-readable and is time-consuming to write.
• Assembly Language: Slightly higher-level than machine language, assembly language uses mnemonics and symbols corresponding to a particular machine’s instruction set, making it somewhat easier to write than raw binary code.

High-level Languages

High-level languages, such as Python and JavaScript, are far removed from a machine’s instruction set. Their syntax resembles English, making them more accessible and easier to understand. Programs written in high-level languages are portable and machine-independent, meaning they can run on any system that supports the language. However, these languages are typically slower, consume more memory, and abstract away low-level hardware details, making them less efficient for tasks that require direct hardware manipulation.

Middle-level Languages

Middle-level languages, such as C and C++, bridge the gap between low-level and high-level languages. They provide a balance by offering control over hardware while also being more human-readable than low-level languages. This combination allows programmers to write efficient code that is still relatively easy to understand and maintain.

By understanding these different types of programming languages and where C fits within this spectrum, you’ll gain a deeper appreciation for the versatility and power of C as you begin your journey into programming.

What Is the C Programming Language?

C is a general-purpose and procedural programming language. As a procedural language, it follows a step-by-step approach to solving problems. This involves using a series of instructions, known as procedures or functions, executed in a specific order to perform tasks and achieve goals. These instructions tell the computer precisely what to do and in what sequence.

C programs are divided into smaller, specific functions that perform particular tasks and are executed sequentially, following a top-down approach. This structure promotes code readability and maintainability.

A Brief History of the C Programming Language

C was developed in the early 1970s by Dennis Ritchie at AT&T Bell Laboratories. Its development was closely linked to the creation of the Unix operating system at Bell Labs. At that time, operating systems were typically written in Assembly language and were not designed for portability.

During the development of Unix, there was a need for a more efficient and portable programming language for writing operating systems. Dennis Ritchie initially created a language called B, which evolved from an earlier language known as BCPL (Basic Combined Programming Language). B aimed to bridge the gap between the low-level capabilities of Assembly and the high-level languages of the time, such as Fortran. However, B lacked the power necessary for Unix development, leading Ritchie to develop a new language inspired by B and BCPL but with additional features. He named this new language C.

C’s simple design, speed, efficiency, and close relationship with computer hardware made it an attractive choice for systems programming. Consequently, the Unix operating system was rewritten in C.

C Language Characteristics and Use Cases

Despite being relatively old compared to modern programming languages, C has stood the test of time and remains popular. According to the TIOBE index, which measures the popularity of programming languages monthly, C was the second most popular programming language as of August 2023.

C is considered the “mother of programming languages” and is foundational to computer science. Many modern and popular languages either use C under the hood or are inspired by it. For instance, Python’s default implementation and interpreter, CPython, is written in C. Additionally, languages like C++ and C# are extensions of C, providing additional functionality.

Originally designed for systems programming, C is widely used in various other areas of computing. C programs are portable and easy to implement, allowing them to run across different platforms with minimal changes. C also allows for efficient and direct memory manipulation and management, making it ideal for performance-critical applications. Furthermore, C provides higher-level abstractions along with low-level capabilities, giving programmers fine-grained control over hardware resources when needed.

These characteristics make C an ideal language for creating operating systems, embedded systems, system utilities, Internet of Things (IoT) devices, database systems, and various other applications. Today, C is used in a vast array of applications across different domains.

How to Set Up a Development Environment for C Programming on Your Local Machine

To set up your local machine for C programming, you’ll need:

1. A C Compiler:
   • If you’re on a Unix-like system (like macOS or Linux), you probably have GCC (GNU Compiler Collection) installed. You can check its version by typing gcc --version in the terminal.
   • If you’re on Windows, consider installing Code::Blocks or setting up Linux on Windows with WSL (Windows Subsystem for Linux).
2. An Integrated Development Environment (IDE):
   • Visual Studio Code (VS Code) is a popular choice. It’s free, open-source, supports multiple programming languages, and runs on all major operating systems.
   • Once you’ve installed VS Code, add the C/C++ extension for enhanced C programming support. You can enable auto-saving for convenience by selecting “File” -> “Auto Save”.

With these tools in place, you’re ready to write, edit, save, run, and debug your C programs effectively. VS Code, with the C/C++ extension, provides a user-friendly environment for C development.

How to Write Your First C Program

1. Open Your Text Editor or IDE: Launch your preferred text editor or IDE. For example, you can use Visual Studio Code, Sublime Text, or any other editor you’re comfortable with.
2. Create a New File: Start a new file and give it a name with a .c extension. For instance, you can name it hello_world.c.
3. Write Your C Code: In the new file, write your C code. For your first program, let’s keep it simple and write a classic “Hello, World!” program. Here’s the code:

                                     #include <stdio.h>

                                      int main() {
printf(“Hello, World!\n”);
return 0;
}

1. This code uses the printf function to display the text “Hello, World!” on the screen. The \n is a special character that represents a newline, so the text is displayed on a new line.
2. Save the File: Once you’ve written the code, save the file.
3. Compile the Program: If you’re using a Unix-like system (like macOS or Linux) with GCC installed, open a terminal, navigate to the directory where your file is saved, and compile the program using the command:

gcc hello_world.c -o hello_world

1. This command tells GCC to compile hello_world.c into an executable file named hello_world.If you’re using Windows with GCC or another compiler, adjust the compilation command accordingly.
2. Run the Program: After successful compilation, run the program. If you’re on Unix-like systems, you can run the program by typing:

./hello_world

1. If you’re on Windows, you can just type hello_world in the command prompt and hit Enter.
2. Observe the Output: You should see the text “Hello, World!” printed on the screen.

What Are Header Files in C?

The line #include <stdio.h> is a preprocessor command that instructs the C compiler to include a specific file. In this case, it tells the compiler to include the stdio.h header file.

Header files are collections of pre-written code and functions that are not part of the core C language. By including these files, you can use the additional functionalities they provide without having to write the code from scratch.

The stdio.h header file stands for standard input-output. It contains function definitions for performing input and output operations, such as gathering user data and printing data to the console. Some of the functions it provides include printf() and scanf().

Including the stdio.h file is essential for the printf() function used later in our program to work. Without including stdio.h at the top of your code, the compiler will not recognize the printf() function.

What is the main() function in C?

The line int main(void) {} defines the main function, which is the entry point of every C program. It is the first function called when the program is executed, making it essential for every C program to include a main() function.

The int keyword in int main(void) {} specifies that the return type of the main() function is an integer. This means that the function will return an integer value. The void keyword inside the parentheses indicates that the function does not take any arguments.

The code inside the curly braces {} constitutes the body of the function. This is where you place the code that you want to run. Any code written inside the main() function will always execute first.

This line serves as a boilerplate and starting point for all C programs, informing the computer where to begin reading and executing the code.

What Are Comments in C?

In C programming, comments are lines of text ignored by the compiler. They are used to provide additional information and explain the logic, purpose, and functionality of your code. Comments enhance code readability and understanding, benefiting anyone who reads or works with it.

Including comments in your code is also helpful for future reference. If you revisit your code after several months, comments can help you quickly recall how it works. Comments are also useful for debugging and troubleshooting. You can temporarily comment out lines of code to isolate and test specific sections without deleting any part of your code.

There are two types of comments in C:

1. Single-line comments: These start with two forward slashes // and continue until the end of the line.
2. Multi-line comments: These start with /* and end with */, allowing you to comment out multiple lines of code.

The printf() Function in C

The printf() function in C is used to print text to the console. For example, in the line printf("Hello, World!\n");, the text “Hello, World!” is displayed on the console (this text is also known as a string).

Whenever you want to display something, use the printf() function. Place the text you want to display inside double quotation marks ("") and ensure it is within the parentheses of the printf() function.

Every statement in C must end with a semicolon (;). The semicolon signifies the end of the statement, much like how a period ends a sentence in English.

What Are Escape Sequences in C?

In the line printf("Hello, World!\n");, the \n at the end is an escape sequence. An escape sequence is a combination of characters that represents a special character within a string. The \n escape sequence creates a newline, moving the cursor to the next line when it appears.

Escape sequences consist of a backslash (\), known as the escape character, followed by one or more additional characters. Another common escape sequence is \t, which represents a tab character and inserts a space within a string.

How to Compile and Run Your First C Program

Consider the following simple C program:

#include <stdio.h>

int main(void) {
// output ‘Hello, World!’ to the console
printf(“Hello, World!\n”);
}

This is called source code, which is written in the C programming language. However, computers do not understand C statements directly. Therefore, the source code needs to be translated into a format that the computer can understand. This is where the compiler comes into play.

The compiler reads the program and translates it into a format closer to the computer’s native language, making the program suitable for execution. When you compile and run this program, you will see the output “Hello, World!” on the console.

Steps of Compilation

The compilation of a C program involves four main steps:

1. Preprocessing: The preprocessor processes directives (like #include) before the actual compilation starts.
2. Compilation: The compiler translates the preprocessed code into assembly language.
3. Assembling: The assembler converts the assembly code into machine code (object code).
4. Linking: The linker combines object code with libraries to produce the final executable program.

The first step in the process of turning source code into an executable program is preprocessing.

1. Preprocessing:
   • The preprocessor scans through the source code to find preprocessor directives, which are any lines that start with a # symbol, such as #include.
   • When the preprocessor encounters these lines, it substitutes them with the corresponding content.
   • For example, when it finds #include <stdio.h>, the preprocessor replaces this line with the actual contents of the stdio.h header file.
   • The output of this phase is a modified version of the source code with all the preprocessor directives resolved.
2. Compilation:
   • After preprocessing, the modified source code is passed to the compiler, which translates it into assembly code.
   • If there are any syntax or semantic errors in the code, the compilation will fail, and these errors need to be fixed before proceeding.
3. Assembly:
   • During the assembly phase, the assembler converts the assembly code generated by the compiler into machine code instructions.
   • The output of this phase is an object file, which contains the machine code instructions.
4. Linking:
   • In the final phase, linking combines the object file generated in the assembly phase with any required libraries to produce the final executable binary file.

To compile your main.c file in Visual Studio Code, follow these steps:

1. Open Visual Studio Code and navigate to the folder containing your main.c file.
2. Open the built-in terminal by selecting Terminal -> New Terminal from the menu.
3. In the terminal, enter the following command to compile your main.c file:

gcc -o main main.c

This command uses the gcc (GNU Compiler Collection) compiler to compile main.c and produce an executable file named main. If there are any errors during compilation, they will be displayed in the terminal, and you will need to address them before the executable can be successfully created.

list the contents of the current directory, use the following command:

This command displays the contents of the current directory, which includes:

The a.out file is an executable containing the binary instructions compiled from the source code.

By default, a.out is the name of the executable file created during the compilation process. To run this file, enter:

This command instructs the computer to execute the a.out file located in the current directory (./). The output from this command will be:

If you prefer to name the executable file something other than the default a.out, for example, helloWorld, use the following command:

In this command, the -o option specifies the output file name, directing the gcc compiler to create an executable file named helloWorld.

To run the newly named executable file, enter:

The output of this command will be:

Remember, each time you modify your source code file, you need to recompile and run your program to see the changes.