Hacker Public Radio

A series focusing on concepts and the basics of programming

void setup() {
    size(480,720);
}
void draw() {
    rect(10,10,80,80);
}
void draw() {
    fill(8,120,90);
    rect(10,10,80,80);
}
void setup() {
    size(480,720);
}

void draw() {
    if (mousePressed) {
        fill(20,120,90);
        ellipse(mouseX,mouseY,25,25);
    } else {
        fill(random(10,120),random(10,80),random(20,200));
    }
}
Started:    11 years, 8 months, 19 days ago (2005-10-10)
Renamed HPR:    9 years, 5 months, 27 days ago (2007-12-31)
Total Shows:    2911
Total TWAT: 300
Total HPR:  2611
HPR Hosts:  286
Days to next free slot: 17
Hosts in Queue: 9
Shows in Queue: 14
Comments waiting approval:  0
Files on the FTP Server:    1
Number of Emergency Shows:  7
Days until show without media:  0
1498246151,369343750,299186950,2911,300,2611,286,17,9,14,0,1,7,0
#!/usr/bin/env python3

### This is a scratchpad file I've created to try out snippets of code in python

# The script below is for use with Python 3
# This script should work out of the box on most systems running a version of Python 3 
# If you happen to have a blinkstick lying about then your can uncomment the blinkstick module
# and uncomment the references at the bottom of the program that call the blinkstick functions
# Regrds, Mr X

# Imported modules
from time import sleep          # used to pause program
#from blinkstick import blinkstick  # used to control blinkstick nano attached to usb port of raspberry pi
import urllib.request           # used to capture hpr webpage content to get the number of HPR shows in the que
import re               # regular expressions, used to find sting in HPR webpage (get_hpr_que)

# These functions control a blink stick nano attached to my raspberry pi USB port #################
# They can be ignored or deleted if you don't have one

def bstick_off():
# Search for all attached blinksticks and turn them all off
    for bstick in blinkstick.find_all():
        bstick.turn_off()   # Turn front blinkstick LED off
        bstick.set_color(channel=0, index=1, name="black")  # Turn rear blinkstick led off
        print("Blinkstick: " + bstick.get_serial() + " turned off")

def bstick_on(colour):
# Turn blinkstick on and set led colour to string value stored in var colour
# valid colours are, black, silver, gray, white, maroon, red, purple, fuchsia, green, lime, olive, yellow, navy, blue, teal, aqua
    for bstick in blinkstick.find_all():
        bstick.set_max_rgb_value(30)        # Sets max blinkstick RGB value to 15, makes LED dimm
        bstick.set_color(name=colour)       # Turn blinkstick on, var colour determines colour
        print ("Blinkstick: " + bstick.get_serial() + " | Colour: " + bstick.get_color(color_format="hex") + " [" + colour + "]")
#hex

def bstick_on_random():
# Turn blinkstick on colour random
    for bstick in blinkstick.find_all():
        bstick.set_random_color()
        print ("Blinkstick: " + bstick.get_serial() + " | Colour: " + bstick.get_color(color_format="hex"))

def bstick_blink_red():
# Flash blinkstick colour red
    for bstick in blinkstick.find_all():
        bstick.blink(name="red")
        print ("Blinkstick: " + bstick.get_serial() + " | Colour: " + bstick.get_color(color_format="hex"))

################################################################################

def get_hpr_que_improved():
# Goto hacker public stats page and extract the number of days to next free slot
# turns on blinkstick LED with colour dependent on the number of days to next free slot in HPR queue

    url = 'http://hackerpublicradio.org/stats.php'  # HPR url for stats page
    try:
        text = urllib.request.urlopen(url).read()   # Try to read hpr stats text
    except:
        print("ERROR: Problem acessing url " + url)     # if error accessing url then return -1
        hpr_shows = -1
        return hpr_shows
    #print(text)    # DEBUG
    text_page = str(text)   # convert text from list to string
    line_begin = text_page.find('Days to next free slot:') # find position of string in page
    line_end = line_begin + 27 # Store line end position (start position + 27)
    line = text_page[line_begin:line_end]  # Capture string line
    #print(line) # DEBUG Print line string
    digit = re.findall(r'\d+',line)         # Find digits in line
    #print(digit[0])    # DEBUG print the 1st digit
    try:
        hpr_shows = int(digit[0])   # convert digit list to integer days
    except:                         # If show numbers not found then return -1
        print("ERROR: Problem getting number of HPR shows in que.")
        hpr_shows = -1
        return hpr_shows

    if hpr_shows > 9:       # If hpr show que > 9 turn on green LED
        print("Turn on green blinkstick LED")
        #bstick_on("green")
    elif hpr_shows > 5:     # Else if hpr show que > 5 turn on blue LED
        print("Turn on blue blinkstick LED")
        #bstick_on("blue")
    elif hpr_shows > -1:    # Else if hpr show que > -1 turn on ref LED
        print("Turn on red blinkstick LED")     
        #bstick_on("red")
    else:
        print("Flash red blinkstick LED")
        #bstick_blink_red() # Else blink LED to show error
    print("The are " + str(hpr_shows) + " days to tne next free slot in the HPR que...")
    sleep(4)
    print("Turn off all blinkstick LED's")
    #bstick_off()           # Turn blinkstick off

# Main program
get_hpr_que_improved()
  ########################################
  #+0****## #+#...###...#..$ ##  #  #    #
  ##+###+## #+++......#...# ##       #   #
  # #.+++++#....#   #      #    #      # #
  #  #+++++#+.+..#  #  #          #      #
  #  #.##.+++#+.### #     #   #   ##     #
  #  ###.+.##++.##     #   ###     #   # #
  ####+.#..#++#.##   #      #####   ##   #
  #++#.#.###+.##    ##       ##    #   # #
  #++++++.##.++.#   #  ##     #  # #  # ##
  #+++++#..##.##      ## #  #### # #    ##
  #+.....#..#.  ##   #      #     ##  ## #
  #+..+.......   # #      #      #  ##   #
  #+...#..###       # #  #          ##  ##
  #.#..#.........# # # # ##### # #    ## #
  #.......##  ##....  #        ###   ##  #
  ##......# ##   ##..#  #####          # #
  #.+.#...###    ###. ##          ##  # ##
  ##.+...#  #      ####      #   ##    # #
  ########################################
  Mouse found the cheese!  :)  Press any key to restart!
Hi, my name is Garjola and you are listening to a contribution to
HPR. This is episode 3 of my programming language series and is entitled
"Getting started with the C programming language"

I am not going to teach you C, but just whet your appetite.

1 Intro
═══════

  • What C is useful for
    • Systems programming
    • Number crunching
    • Graphics
    • Embedded systems
      • Arduino
  • Advantages
    • speed
    • fine grained control of the memory management
    • close to the metal
    • the portable assembly language
  • Drawbacks
    • fine grained control of the memory management
    • close to the metal
    • the portable assembly language

2 History of the language
═════════════════════════

  • developed by Ken Thompson and Dennis Ritchie between 1969 and 1973
    at AT&T Bell Labs.
  • The origin of C is closely tied to the development of the Unix
    operating system, originally implemented in assembly language on a
    PDP-7 by Ritchie and Thompson, incorporating several ideas from
    colleagues. Eventually they decided to port the operating system to
    a PDP-11. B's inability to take advantage of some of the PDP-11's
    features, notably byte addressability, led to the development of an
    early version of C.

3 Uses
══════

  C is often used for "system programming", including implementing
  operating systems and embedded system applications, due to a
  combination of desirable characteristics such as code portability and
  efficiency, ability to access specific hardware addresses, ability to
  pun types to match externally imposed data access requirements, and
  low run-time demand on system resources. C can also be used for
  website programming using CGI as a "gateway" for information between
  the Web application, the server, and the browser. Some reasons for
  choosing C over interpreted languages are its speed, stability, and
  near-universal availability.

  One consequence of C's wide availability and efficiency is that
  compilers, libraries, and interpreters of other programming languages
  are often implemented in C. The primary implementations of Python
  (CPython), Perl 5, and PHP are all written in C.

  Due to its thin layer of abstraction and low overhead, C allows
  efficient implementations of algorithms and data structures, which is
  useful for programs that perform a lot of computations.

  C is sometimes used as an intermediate language by implementations of
  other languages. This approach may be used for portability or
  convenience; by using C as an intermediate language, it is not
  necessary to develop machine-specific code generators.

  C has also been widely used to implement end-user applications, but
  much of that development has shifted to newer languages.

4 Characteristics of the language
═════════════════════════════════

  • imperative, compiled, static, weakly typed
  • structured programming
    • Uses functions but it is not functional, but rather procedural
    • control flow if/else, for, while
    • curly braces, semi-colons
  • all parameters are passed by value and references are simulated
    using pointers
  • A program is a function called main

5 Tooling and environment
═════════════════════════

  • editor
  • compiler
    • makefiles for convenience, although higher level tools such as
      autoconf/automake or cmake exist
  • debugger
  • IDEs
  • gnu tools for everything
    • emacs, pico, gedit, vi
    • gcc, clang
    • gnumake
    • gdb, xgdb, ddd
    • kdevelop

6 Hello World
═════════════

  #include <stdio.h>

  int main(void) { printf("hello, world\n"); return 0; }

7 How to make a C program
═════════════════════════

  • Write your main function into a file called myprogram.c
  • compile your program
    • gcc -o myprogram myprogram.c
  • if you use other libraries than C's standard library, you will need
    to use a linker, like ld

  Examples taken from An Introduction to GCC
  by Brian J. Gough, foreword by Richard M. Stallman
  [http://www.network-theory.co.uk/docs/gccintro/]

  The classic example program for the C language is Hello World. Here is
  the source code for our version of the program:

  #include <stdio.h>

  int main (void) { printf ("Hello, world!\n"); return 0; }

  We will assume that the source code is stored in a file called
  ‘hello.c’. To compile the file ‘hello.c’ with gcc, use the following
  command:

  $ gcc -Wall hello.c -o hello

  To run the program, type the path name of the executable like this:

  $ ./hello
  Hello, world!

8 Pointers!
═══════════

  C supports the use of pointers, a type of reference that records the
  address or location of an object or function in memory. Pointers can
  be dereferenced to access data stored at the address pointed to, or to
  invoke a pointed-to function. Pointers can be manipulated using
  assignment or pointer arithmetic.  The run-time representation of a
  pointer value is typically a raw memory address (perhaps augmented by
  an offset-within-word field), but since a pointer's type includes the
  type of the thing pointed to, expressions including pointers can be
  type-checked at compile time.

9 The standard library
══════════════════════

  • just use man!
  On Unix-like systems, the authoritative documentation of the actually
  implemented API is provided in form of man pages. On most systems, man
  pages on standard library functions are in section 3; section 7 may
  contain some more generic pages on underlying concepts (e.g. man 7
  math_error in Linux).

  apropos sqrt |grep \(3\) man 3 sqrt

  man 3 qsort history

  • the not-so-standard libraries
    • gsl
    • gtk
    • X

10 Languages of the C family
════════════════════════════

  • C++, ObjectiveC, Java, C#, Go

11 Resources
════════════

  • [http://www.nongnu.org/c-prog-book/] : Learning GNU C by Ciaran
    O'Riordan.

for x in range(1, 10):
       print(x)

for x in range(1, 11):
       print(x)

y = 0
for x in range(1,101):
       y = y + x
print(y)

y = 0
x = 1
while x < 101:
       y = y + x
       x = x + 1
print (y)

x = 0
y = 0
z = 1

while z < 100:
       x = y
       y = z
       z = x + y
       print (z)

x = 0
y = 0
z = 1

while z < 100:
       print (z)
       x = y
       y = z
       z = x + y

x = 0
y = 0
z = input('What number do we start from?')
i = input('And up to which number should we calculate')

while z < i:
       print (z)
       x = y
       y = z
       z = x + y

print ("Hello World")

print ("Hello \"World")

x = 1
print (x)

x = 1
x = x + 5
x = x * 7
print (x)

x = 1 + 5 * 7
print (x)

x = (1 + 5) * 7
print (x)

# This is a comment
x = (1 + 5) * 7
# print ("5")
print (x)

x = "Hello World"
print (x)

x = "Hello"
y = "World"
print (x+y)

x = "Hello"
y = "World"
print (x + " " + y)

sFirstName = "John"
sSurname = "Smith"
print ("Dear " + sFirstName + " " + sSurname)

x = 13
sFirstName = "John"
sSurname = "Smith"
if x < 12:
	print ("Good Morning " + sFirstName + " " + sSurname)
else:
	print ("Good Evening " + sFirstName + " " + sSurname)

x = 11
sFirstName = "John"
sSurname = "Smith"
if x < 12:
	print ("Good Morning " + sFirstName + " " + sSurname)
else:
	print ("Good Evening " + sFirstName + " " + sSurname)
print ("When does this get printed?")

In-Depth Series

Programming 101

Links

Episode 1: History and Basic Types

Explain who you are and what you do.

Start to go into the history of C and explain where it came from.

Abstract

Explain Types and their meanings

int:

Int Specifiers

char

Note about the ascii table

float

Double

Arrays

Strings

CATRPI

Hacker's Delight by Henry S. Warren Jr.

ARM ARM

ARM TRM

dwelch67's bare metal repository

Links

Programming languages 2 - Getting started with Python

2 Installation

3 Syntax and semantics

4 Interpreter

5 Standard library

6 Documentation and tutorials

1 Wikipedia sources:

2 Resources for learning to program

2.1 Easy

2.1.1 List of resources on Wikipedia

2.1.2 The Python tutorial

2.2 Intermediate

2.2.1 Structure and interpretation of computer programs