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Introduction to C

note

These C notes are from the Computer Science programming course I attended at university, so they will cover more broad and advanced topics.

Instead, I wrote the C++ mini-guide in earlier chapters during high school, while attending a simpler programming course, so it is likely more beginner-friendly. Consider starting with that guide first if you are new to programming.

This chapter introduces the fundamental concepts of the C programming language.

Characteristics of C​

Some of the main characteristics of C are:

  • Procedural: programs are structured as a set of "procedures" or functions that operate on data.
  • Compiled: the source code is transformed by a program called a compiler into machine language, specific to a particular machine, creating an executable program.
  • Declarative and typed: every variable (a container for data) has an associated type (for example, integer, floating-point number, character). The developer must declare the type of each variable before using it.

Even though there's no clear line between abstraction levels in programming languages, C can be considered a mid-level language. It sits between high-level languages like Python or Java, which hide many hardware details, and low-level languages like assembly, which works directly with the processor's instructions and are highly machine dependent. This gives C a good balance between hardware control and ease of use.

Brief history​

C was created by Dennis Ritchie at Bell Labs in the early 1970s. It is closely tied to the Unix operating system, for which it was originally developed. It was designed for practical system programming, balancing low-level hardware access with portability.

Brian Kernighan's handwritten "Hello, World!" program from 1978 became an iconic symbol of C:

Hello World Brian Kernighan 1978.jpg

By Brian Kernighan - https://www.artsy.net/artwork/brian-kernighan-hello-world, CC BY-SA 3.0, Link

Over the years, C has been standardized several times:

  • C89/C90 (1989-1990): the first widely adopted standard;
  • C99 (1999): added features like variable-length arrays;
  • C11 (2011): introduced multi-threading support and more;
  • C17 (2018): technical corrections and clarifications to defects in C11.

This guide focuses on C99 for its broad compatibility, possibly touching upon C11 and C18. Not all compilers fully support the latest standards, so chose the right one based on your necessities.

Why use C?​

C is used in a wide range of applications:

  • Operating Systems like Linux are written primarily in C.
  • Embedded Systems such as microcontrollers, due to its efficiency and direct hardware control.
  • Drivers that allows the operating system to communicate with hardware are often written in C.
  • High-Performance Libraries used by other languages (for example, numerical libraries for Python) are written in C.
  • WebAssembly: C can be compiled into WebAssembly, a format that allows high-performance code to run in web browsers.

With great power comes great responsibility​

C offers great control over computer resources, but this freedom also makes it easy to introduce errors (bugs) that can cause unexpected behavior or program crashes.

Making mistakes is easy and subtle – the language does not allow the compiler to catch all the "oversights" you might have made. Errors can cause much more serious damage – you don't have an interpreter (like Python) or a virtual environment (like Java) to help you.

Some key principles (you will understand them as you learn the language):

  • Always verify that input data is valid and that functions return the expected values;
  • Use "safe" functions;
  • Engineer your code well;
  • Do not underestimate warnings, treat them as errors and fix them.

Development Tools​

To write, compile, and run C programs, we'll need:

  • Text Editor: you can use a simple text editor (like Notepad on Windows or TextEdit on macOS), but a more advanced editor with features like syntax highlighting and autocompletion is recommended (like VS Code, Sublime Text, Vim, Emacs).
  • Compiler: the most popular compiler is GCC (GNU Compiler Collection), available on Linux, macOS (through tools like Xcode or Homebrew), and Windows (through MinGW or Cygwin).
  • Debugger: it allows you to run the program step-by-step, inspect the contents of variables, and identify errors. GCC includes GDB, a command-line debugger. Many IDEs (integrated development environments) offer debuggers with a graphical interface.
  • Makefile: a tool for managing the compilation of C projects.

The easiest way to start is probably with Visual Studio Code, which is the IDE I'll be using for these notes.

After installing its C/C++ extension (which doesn't include a compiler or debugger), follow this guide to install the C and C++ compiler on your computer.

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