quartz/content/notes/08-intro-to-c.md

title	aliases	tags	sr-due	sr-interval	sr-ease
08-intro-to-c		lecture cosc204	2022-08-08	3	250

Developed 1972 for Unix

• widely used
  • compilers esxist for most OSs and architectiures
• diverse use
  • OSs, device drivers, protocol stacks
  • less so for application software
• low level
  • language features map to CPU features
• not Object Oriented
  • no classes etc

“C is an imperative procedural language supporting structured programming, lexical variable scope, and recursion, with a static type system. It was designed to be compiled to provide low-level access to memory and language constructs that map efficiently to machine instructions, all with minimal runtime support. Despite its low-level capabilities, the language was designed to encourage cross-platform programming. A standards-compliant C program written with portability in mind can be compiled for a wide variety of computer platforms and operating systems with few changes to its source code.” - wikipedia

#include <stdio.h>

int main(int argc, const char *argv[])
{
	puts("Hello World");
	return 0;
}

#include

java uses .class files, C uses .c and .h

• .c for implementation
• .h for extern declarations (similar to public)

java uses import, C uses #include

#include <stdio.h>
#include "myfile.h"

• #include literally includes the file with the given name right there into the file eing compiled
• in hello_world.c we include stdio.h so we can call puts()

Routines

int main(int argc, const char *argv[])
{

}

routines can be scoped to just the source code file

• static int eleven(void

routines must be declared bfore being used

• extern int eleven(void):

if, const, for, while, do, case etc same as java

Types

char
float, double
int, short, long
signed, unsigned
void

sizeof

• to find out size of any type (built-in or user defined)

stdint

Structs

• like classes but without methods
• all fields public
• you can have structs in structs

typedef

• any type can be given a new name using typedef

typedef struct
	{
		float x, y, z;
	} coordinate;

static

• the scope of this routine is local to this file
• this variable maintains its value between calls

void keeper(void) { 
	static uint64_t times_called = 0; 
	times_called++; 
	printf("Count:%llu\n", times_called); 
}

typecasting

like java

uint64_t y = 1024;
unit32_t x = (unit32_t) y;

Keywords to ignore

• auto
  • all local variables are auto
• register
  • deprecated

keywords to think about

• volatile
  • do not optimize accesses to this variable
    • might be changed by another thread or a harware event
  • you're likely to see this in operating system souce code
  • you're likely to see this in multithreaded programs