The C Programming Language

Introduction

C is a compiled and general-purpose programming language, closely associated with the Unix system
the language is not tied to any one operating system or machine
useful for writing compilers and operating system, but also to write major programs in many different domains
C provides a variety of data types, the fundamental ones are characters, integers and floats
in addition, there is a hierarchy of types created with pointers, array, structures and unions
expressions are formed from operators and operands, any expression can be a statement
provides the fundamental control flow constructions like statement grouping, decision-making (if/else, switch), looping (for, while, do) and early loop exit (break)
provides no operations to deal directly with composites such as strings, sets, lists or arrays
no heap or garbage collection
no I/O facilities and no file access methods
offers only straightforward, single-threaded control flows
not strongly-typed, but its type checking has been strengthened

#include <stdio.h>

int main()
{
  printf("hello world\n");
}

first, compile: gcc hello-world.c
second, run: ./a.out
#include <stdio.h> // standard I/O library
%d to print a variable with a digit/int type
semicolons at the end of statement
most used basic data types: int, float, char, short, long, double
integer divison truncates
#define name value for magic numbers, e.g. #define MAX 300
text I/O is dealt with as streams of chars, a text stream is a sequence of chars divided into lines, every line ends with a newline char
getchar() reads the next input char
putchar(c) prints the content