The C Programming Language

• created in the 1970s (BCPL 🠊 B 🠊 C) by Dennis Ritchie^🌐

• general-purpose, procedural (imperative) programming language

• simple, small, relatively low-level

• close to the hardware (von Neumann architecture), but still portable

• even today used for system programming (OS kernels), embedded systems, device drivers, performance-critical applications

• associated with the UNIX operating system (today Linux, OSX, BSD, etc.)

• bootstrap language for many other languages (e.g. Python)

The K&R book ("The C book")

A book on C programming, written by Brian Kernighan^🌐 and Dennis Ritchie.

It is a classic.

The program structure

• C program: set of functions and variables

• main() is the entry point, called by the OS

Data types

fundamental:

• characters: char (byte),

• signed/unsigned integers: int (short, long)

• floating point numbers: float, double

derived:

• arrays [..]

• pointers (memory addresses) *

• structures struct

• unions union

• enumerations enum (named integer constants)

special:

• bit fields

Operations

over fundamental data types

• arithmetic: +, -, *, /, %

• logical: &&, ||, !

• bitwise: &, |, ^, ~, <<, >>

• assignment: =, +=, -= ,*=, /=, %= ,&=, |=, ^=

• comparison: ==, !=, <, >, <=, >=

over derived data types

• arrays: indexing [i]

• pointers: dereferencing *, pointer arithmetic +, -

• structures, unions, bit fields: member access .

• pointers: dereferencing and member access ->

Expressions

• arithmetic: a + b, a * b, a / b, a % b

• logical: a && b, a || b, !a

• bitwise: a & b, a | b, a ^ b, ~a, a << b, a >> b

• assignment: a = b, a += b, a -= b, a *= b, a /= b, a %= b, a &= b, a |= b, a ^= b

• conditional: a ? b : c

• function calls

Statements

Statements can be:

• simple, terminated by semicolon ;

• compound (block), enclosed in braces { }

Expressions are statements, but not all statements are expressions:

• declaration: int a;, float b;

• iteration (loop): for, while, do ... while

• conditional (selection): if, switch

• jump: break, continue, return, goto

• labelled: label, case, default

• empty (null): ;

Functions

• declaration: return type, name, parameters

• definition: return type, name, parameters, body

• instead of procedures: functions with return type void

Declarations are optional.

Other features

All additional features: input/output, memory management, multithreading … must be implemented in a library. Standard libraries:

• stdio.h

• stdlib.h

• string.h

• math.h

• pthread.h, etc.

Program

Two kinds of source files:

• header files (.h) for declarations,

• source files (.c) for definitions.

Preprocessor and macros

Preprocessor is one of the most powerful features of C. It is purely textual, runs before the compiler and handles directives, macros, and conditional compilation.

• Directives: #include, #define, #ifdef, #ifndef, #else, #endif.

• Macros are used for text substitution, mostly for constants, inline functions, fragments of code, etc.:

  • #define PI 3.14159

  • #define SQUARE(x) ((x) * (x))

Hello, World!

Hello, World! is the first program that is traditionally used as an introduction to a programming language. It prints "Hello, World!" to the console.

It is a kind of a tradition started by Brian Kernighan.

See

1. docker

2. hello