C

A.K.A. High-level assembler

For when you gotta go fast

Created by jyn with reveal.js

5 minute history

C is the oldest programming language still widely used (except maybe COBOL)
In 1972, Dennis Ritchie had to program on this machine:

His compiler was fast and free so people used it
Called high-level assembler because it is very close to how a CPU operates

What is C good for?

Going fast
Talking directly to hardware (memory-mapped I/O)
Making system calls and FFI calls

Don't worry if you don't know these words yet

Enough meta, what does C look like?

Threaded Web Server

(demo goes here)

Preprocessor

#include — C doesn't have imports, it just puts an entire file inside of your file
#define A 1 — for when you want to be sure things are inlined
#ifdef — conditional compilation

Header files

C used to use a single-pass compiler, so it has to be very stupid
The compiler only knows the type of a function if you declare it before you use it
Also, C doesn't have public/private, static is the poor man's private

Pointers!

Pointers hold the address in memory of a variable

picture credit: stackoverflow.com

What's the difference?

int f(int i) {
  i = 1;
}

int f(int *p) {
  *p = 1;
}

Arrays in C are pointers

Have to know the length ahead of time
Array index is offset from a pointer
This is why arrays are 0-indexed!

int main() {
  int a[] = {1, 2, 3};
  int i;
  // these are all equivalent and set i to 1
  i = a[0];
  i = *a;
  i = *(a + 0);
  i = *(0 + a);
  i = 0[a];
  // this will not compile
  i = a; // error: assignment makes integer from pointer
}

Strings in C are arrays

No classes!
Have to know the length of a string somehow
Denoted by null character '\0'

picture credit: dyclassroom.com

How do you return multiple things in C?

In Java, you return a class
In Python, you return a tuple
```
(a, b)
```
In C, you have output parameters

Signals

(demo goes here)

picture credit: gerhardmueller.de. You can tell I was really having trouble finding pictures.