Basic C

History

Developed by Dennis Ritchie between 1969 and 1973
- With Brian Kernigham (K&R C)
- Book: The C Programming Language
One of the most widely used languages of all time
Named C because its features were derived from "B"
- "A stripped down version of BCPL"
Influenced many languages, most notably C++
- C++ is an extension of C
Heavily incorporated with Unix development
- Before C, Unix was written in assembly

C is an imperative (procedural) language
Design to provide low-level access to memory
Requires minimal run-time support
Supersedes many applications that previously were in assembly
Awesome for cross-platform compiling
- mips, ia64, x86[_64]
Used in a wide variety of applications, including microcontrollers and supercomputers

Variables are create by announcing the type, followed by the name, and ended with a semicolon
So this would create an integer named foo:

!cpp int foo;
You can assign a value to the variable directly with

!cpp int foo = 100; foo = 100;
Functions are declared by specifying a return type, with arguments in paren's, and the code block in curly braces.

!cpp int main(int argc, char *argv) { return 0; }

Some basic C source:

!cpp
#include <stdio.h>
int main(int argc, char *argv[])
{
	printf("Hello World!\n");
	return 0;
}

Output:

Hello World!

Source is included in this repository as hello.c

!cpp
#include <stdio.h>

!cpp
int main(int argc, char *argv[])

The infamous main function
int is a base C data type
- At least 16 bits in size, depends on architecture.
char is another base type
- Smallest unit of the C data types
In this case the value returned, of type int, is the exit status
A return status of EXIT_SUCCESS == 0, is a good thing
- A return of > 0 is usually an error

!cpp
int main(int argc, char *argv[])

argc (Argument count): A guaranteed non-zero number
- argv[argc] is guaranteed to be null
argv (Argument Array): An array of arguments (char arrays) that have been passed to the executable

See that char *argv[]? Think of it as a pointer to a list of arrays.
Take a deep breath
Remember that C can directly access values at an address
The size, or rather the amount of things we are pointing to doesn't matter
As long as you play nice, you won't get a segfault.
Using this idea, we can point to the start of a series of char arrays
In int main(int argc, char *argv[]), the argv is just such a thing
By getting argv[0], we are retrieving a pointer to the first argument provided to the program

So:

!cpp
int foo;
int *bar;
bar = &foo;

char *str = "Hello World!";
char baz = str[0];

The & operator retrieves the address for the variable
We can dereference a pointer, or retrieve its value by putting an asterisk in front of it

!cpp
printf("Hello World!\n");

If you passed in str from the previous example, that would be fine:

!cpp
printf(str);

!cpp
return 0;