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C Language

The Evolution of C

  • 1972: The C programming language is created by Dennis Ritchie
    • Dennis Ritchie worked at Bell Labs
    • It was named C because it was the successor of B
    • It was intended to be used to create programs for the Unix operating system, however soon the Unix kernel itself was rewritten in C
  • 1978: The C Programming Language is published
    • The "hello world" idea started on this book
  • 1989: ANSI C ratified
  • 1999: "C99" released
    • new data types
    • single line comments
    • others
  • 2011: "C11" released
    • generic macros
    • multi threading
  • 2018: "C18" released
    • minor technical corrections to the language specification

The Lowest High-level language

Assembly code is architecture specific, so it's not very portable.

The two problems that C solved that led high adoptions:

  • Syntax that works at a higher level of abstraction
  • Code portability (which was made possible by the creation of C compilers for different platforms)
                                        [--Source Code--]

                    [--C Source Code --]   [--Compiler--]

[--Assembly Code--]   [--C Compiler--]  [-- Runtime/VM--]

[----------------------Machine Code---------------------]

Advantages of using C

  • Relatively small: about 40 reserved words
  • fast and low level access to memory
  • good for building
    • Operating Systems
    • cross-platform and fast apps
      • example: Git
    • embedded systems

Programming Embedded Systems

C has become the defacto tool for programming embedded systems.

Writing C Code

You only need two things to start writing C: a compiler and and editor.

Compilers

  • GNU Compiler Collection (GCC)
    • supports: C, C++, Go
  • Clang
  • CL (Visual Studio)

Editors and IDEs

There are many options, but these are some of the features you should look for:

  • syntax highlighting
  • code completion
  • for larger projects, IDEs will come in handy:
    • debugging
    • performance profiling
    • test runners

Popular IDEs:

  • xCode - macOS
  • Visual Studio - Windows
  • CLion - Windows, macOS, Linux
  • Visual Studio Code

Compiling C Program

C File Types

Header files

// products.h

void display_product(int);
double get_price(int);

Header files exist to share declarations between source code files. You include your functions in a header file and then include that file in the source files your you want to call the functions.

Source code files

// inventory.c

void print_inventory(int id) {
    display_product(id);
}

Compiling

program.c ----compiler---> program.obj --linker---> executable

There are tools that automate this process, such as Make.

A Makefile contains all the steps required for the build.

Writing Procedural Code

C is a procedural language that uses procedures as the building blocks.

Procedures are also known as methods, functions or routines.

Some Important Applications of C

  • Supercomputers. They are powered by the Unix/Linux operating system, and their kernel is written in C.
  • Embedded Systems and Hardware-level Programming
  • Mars Curiosity Rover Flight Software
  • The Linux kernel is almost entirely written in C.
  • Highly-optimized Libraries (e.g. FFTW)