Notes on the C Programming language, many from the "C programming for beginners" course on Udemy.

• is two steps: pre-processing and the actual compilation.

• the compiler translates assembly lang statements into actual machine instructions

• the output from the compiler is known as object code (.obj or o extension)

• common command to compile is : cc -c myprog.c or gcc -c myprog.c (the latter is the GNU c compiler.)

• after creating the object code, it can be linked.

• linking gets all dependencies in place and builds the executable file. All .o files will be linked.

• This usually happens at the same time as compiling when you use an IDE.

• Linux will spit out a myfile.out

• it's fairly unique to C, and is advantageous

• makes programs easier to read, modify and port.

• it's part of the compilation process; happens before the program is analyzed.

• preprocessor commands can be anywhere in your code but are usually at the top.

• Preprocessor statements are identified by the # sign (a "preprocessor directive".)

• Preprocessors can be used to build your own library files, constants, macros,

• can make more powerful programs with conditionals: #ifdef, #endif, #else, #ifndef etc.

• is a preprocessor directive used in all C programs.

• include files are usually header files b ecause it is usually included at the head of the document.

• has a .h extension.

• using #include "json.h" means look in the current direcotry.

• using #includ <json.h> means look in the standard system directories.

• they define information about some of the functions that are provided by that file.

• header files usually have function prototypes (names of functions), typedefs, and constants.

• executable code doesn't (usually) go into a header file.

• used for displaying variables as output.

• they specify the type of the data that you want to display.

• ex: int sum = 89; printf("The sum is %d\n", sum)

• for each type, printf expects a certain kind of datatype (%i, %e, %c) etc.

• AND, &, ~OR~;, tests and set individual bits in an integer variable.

• These operate on the bits in integer values.

• less commonly used.

• Why? - it can store a lot of data in it.

• You could use a single integer variable to store several characteristics of an "object"

  • you could use one bit, in an integer (which is made of multiple bits) to indicate on/off data.

  • a byte is 8 bits; an integer is usually 4 bytes (and thus, 32 bits)

Constants can be created using #define, const (in c90) or enums.

// Using the preprocessor (note, no use of "=")
#define FOO 0.015

// using  const
const int foo 15

• there is no standard datatype for strings in C.

• strings are stored in an array of type char.

• Remember to add an extra length when declaring the string length - to make room for a null terminator (\0)

# you can put "7" in the array, but you should avoid this. Let the compiler set the size for you.
# bad
char word[7] = {"Hello"}


# better
char word[] = {"Hello"}

• because strings are char arrays, you can't use operators on then.

  • thus, determing if two strings were the same would require checking each char at each point in the array.

  • and so, there are string functions in the standard library to avoid having to do this manually.

• Use #include <string.h> to include string library functions.

  • strcpy, strncopy- to change or modify a string. (try and use strncopy, it's safer)

  • strlen

• pointers are a variable that store an address (in hexadecimal, usually)

• the value of a pointer, is the address of another location in memory, that can contain a value.

• A lot of string functions return pointers.