Introduction

• Look at C and C++
• Look at compilation process
• Representing of code on Micro controller

In the Beginning, there was assembly.

; linker puts the entry point here:
_start:

; Write the string to stdout:

    mov edx,len ;message length
    mov ecx,msg ;message to write
    mov ebx,1   ;file descriptor (stdout)
    mov eax,4   ;system call number (sys_write)
    int 0x80    ;call kernel

; Exit via the kernel:

    mov ebx,0   ;process' exit code
    mov eax,1   ;system call number (sys_exit)
    int 0x80    ;call kernel - this interrupt won't return

Amazing Grace

The Invention of High Level Languages

• Admiral Grace Hopper.
• Invented the Compiler and COBOL

It’s much easier for most people to write an English statement than it is to use symbols. So I decided data processors ought to be able to write their programs in English, and the computers would translate them into machine code.

Monolithic Programming

• Code in one huge block
• Use of GOTO statements

Monolithic

C (Procedural)

• C has a procedural view of programming
  • Focus on the Functions we have to perform
• Improvement as we break code into reusable, logical, chunks

C

C++ (Object Orientated)

• C++ Introduced classes
  • Object orientated
  • Focus on both the functions and the data associated with them.

C++

C and C++

• The basics are similar
  • Pre-defined, strongly typed variables
  • Syntax is very similar

In MBED OS

• Differences are less pronounced
  • “C with Classes”
• No desktop style stdlib
  • use mbed.h

Learning C

• Can be a bit intimidating depending on background
  • Typing, Pointers etc unfamiliar to Python users
• Secret is to:
  • Think like a programmer
  • Practice

Thinking like a programmer

• We shouldn’t learn Python / C / Java
• Instead basic building blocks of a program
• Syntax is just “magic words” to achieve this.
  • (Yes there are language specific quirks)

What Makes a Program

1. Importing Libraries
2. Defining and using Variables
3. Selection and Iteration
4. Classes and Function Calls

What makes a program

• Think about the Logical flow of what we want to do
  • How do we represent that in our building blocks
• Implement in language specifics

Practice

I hear and I forget. I see and I remember. I do and I understand.

Confucius

C Program Components

• Preamble: Import libraries, setup global
• Main(): Entry Point to the program

Hello world.

#include 

int main() {

  // put your setup code here, to run once:
  //Setup the LED1 pin to be a digital output called ledOne
  DigitalOut ledOne(LED1);


  while(1) {
    // put your main code here, to run repeatedly:

    printf("Loop\n");
    ledOne = 1;
    ThisThread::sleep_for(500ms);
    ledOne = 0;
    ThisThread::sleep_for(500ms);
  }
}

Preamble

• Used to import relevant libraries
• Used to set global variables.

Program Code

• Can be broken into different functions
• main() is our entry point
  • tells the program where to start.

Compiled Code

• C is a compiled language
  • Start with high level “human readable” representation
  • Use a compiler to turn this into machine level representation

Code Compile Process

• Lexing: Break high level code into a set of tokens
• Parsing: Derive meaning from tokens, and build AST
  • Intermediate Stage Use AST to generate intermediate code (for example ASM)
• Compile Turn AST into machine level language.

C: General Syntax

C: Tokens

Tokens: Identifiers

• A name we have defined for something
  • Variables / Constants
• Case Sensitive

Tokens: Identifiers

• int led;
  • led is the identifier
• char* thestring[50];
  • thestring is the identifier

Tokens: Literals

• A data value expressed directly in the code
  • int led=5;
    • Set the value of led to 5
  • string name="dan";
    • Set the value of name to dan
  • char letter=0x42;
    • Set the value of letter to 0x42 (hex representation)

Tokens: Operators

• A symbol representing an operation to be performed.
• arithmetic, logical, assignment etc.
  • int a = 5+1
    • = is assignment
    • + addition
  • 1==1
    • == Check for equality.

Tokens: Keywords

• Have special meaning in the language
  • Declaring Variable Types
  • Iteration and Selection
• Cannot be used as Identifiers

Tokens: Keywords

• int foo
  • Declare foo to be of type int
• while (1)
  • Next block of code is a while loop
• if (foo == 1)
  • Selection operator

White space

• Not “Important” to C (unlike python)
  • Still important for readability
  • White space (IE Indentation) is a good idea
• See https://en.wikipedia.org/wiki/International_Obfuscated_C_Code_Contest

White space

int x=5; while (x > 0){ printf("Value of X is %d\n", x); }

White space

int x=5;
while (x > 0){
    printf("Value of X is %d\n", x);
    }

Punctuation

• Used to represent sets of instructions
  • Statements end in ;
  • Blocks enclosed in { }

Punctuation

• Common cause of problems
  • Especially when switching from Python etc.
• Compiler will do its best to help us with error messages.

src/main.cpp: In function 'int main()':
src/main.cpp:14:5: error: expected ';' before 'ledOne'
     ledOne = 1;

Common Tasks

• How do we do common programming tasks in C:
  • Defining Variables
  • Selection and Iteration

Defining Variables

• C is strongly typed
• Means we need to tell compiler what our variable is expected to be
  • Contrast with weakly typed python

Defining Variables

• Behind the Scenes
  • Part of function preamble, and process control
  • Space is pre-allocated on the stack for each variable

Variable Size

• Can be an issue in embedded development
  • Different target boards may have different widths
• Should be OK if we use a specific chipset (ie STM32)

Variable Size

• Byte 8 Bits
• Half Word 16 Bits
• word 32 Bits
• dword 64 Bits

C: Variable Types

• int Integer (whole) numbers
• float Floating point (decimal) numbers
• char Single Characters
• char* Character Array

C: Variable Types

Selection

• Used when we have a choice to make.

if (variable == value){
   //do something
   }
else{
   //Do something else
}

Iteration

• Used when we want to repeat ourselves.
• Two main types
  • for if we know the number of times we will repeat
  • while keep going until a condition is met.

Iteration: For Loops

for (int x=0; x<10; x++){
   //do something
}

Iteration: While Loops

int x=0 //Start condition
while (x<10){
  //do something
  x+=1 // DON'T forget to update the condition
}

Functions: Allow us to break code into Logical blocks

int add(int first, int second){
    int out = first+second;
    return out;
    }

Classes

class flasher {
   //variables go here

   //Methods go here
   int add(int first, int second){
     ...
   }

}

Q&A Time

• Questions?