Programming - Procedures, Architecture, & Tools(1)

Administrivia

Practice Web Page - http://www.cs.tau.ac.il/~efif/courses/Programming_Fall_04

Overview of the course

• Basic computer architecture
• C programming

Basic model

Programming

• Understanding programming requires that you understand computers
• A computer is an an idiot savant
• everything done using numbers
  • Store and retrieve numbers quickly and accurately
  • Add, subtract, multiply, and divide (also fast and accurate)
    • more complex math - combination of atomic operations
  • Compare numbers (with 0)
  • Follow a list of instructions, and jump around in the list
  • interaction with peripheral devices
    • output: graphics cards and printers
    • input: keyboards, mice, joysticks
    • all sorts of specialized devices

Terminology

• bit: binary digit
• byte: a group of 8 bits. Can represent 256 values (0 to 255 or -128 to 127).
• nibble (obsolete): half a byte
• word: a group of bytes that a specific computer is optimized for working with (usually 4 or 8)
• kilobyte (K or KB): 1,000 bytes, or sometimes 1,024 bytes (2¹⁰)
• megabyte (M or MB): 1,000,000 bytes, or sometimes 1,028,576 bytes (2²⁰)

Inside the computer…

• Everything is bits
• Bits are always grouped into bytes, words
• Every byte is numbered sequentially called an address, which are numbers themselves

computer instructions

• Computers execute instructions
• Instructions are numbers
  • memory access (get/put)
  • arithmetic (add, subtract, multiply, divide)
  • compare values (equal, greater than, less than)
  • change the order instructions are executed in
    • often based on the result of a comparison

what kinds of numbers do computers work with?

• Instructions
• Addresses
• Data
  • integers
  • real numbers
  • text
  • all sorts of other things

what is a computer program?

• A sequence of processor instructions designed to achieve a specific purpose
  • Computers execute programs sequentially
  • Unlike, say, a shopping list
  • More like driving directions
    • each instruction depends on the last one being completed
• Each instruction has a numerical code
• Examples:
  • Get some data from memory
  • Add two numbers
  • If two numbers are equal, jump to a different part of the program
• To us, it all just looks like numbers
• Instructions are numbers
• Random numbers can be executed
  • but will not be a program

  00401040 55 8B EC 83 EC 5C 53 56 57 6A 00 FF 15 B8 C2 42
  00401050 00 89 45 FC 83 7D FC 00 7D 1B 68 0F 10 40 00 68
  00401060 14 61 42 00 B9 E8 99 42 00 E8 32 05 00 00 8B C8
  00401070 E8 90 FF FF FF 8D 45 EC 50 8B 0D 50 8D 42 00 51
  00401080 FF 15 C0 C2 42 00 89 45 FC 83 7D FC 00 7D 20 68
  00401090 0F 10 40 00 68 F8 60 42 00 B9 E8 99 42 00 E8 FD
  004010A0 04 00 00 8B C8 E8 5B FF FF FF E9 9C 00 00 00 68
  004010B0 0F 10 40 00 68 D8 60 42 00 B9 E8 99 42 00 E8 DD
  004010C0 04 00 00 8B C8 E8 3B FF FF FF 8D 55 E4 52 68 28
  004010D0 71 42 00 6A 01 6A 00 68 18 71 42 00 FF 15 C4 C2
  004010E0 42 00 89 45 FC 83 7D FC 00 7C 1D 68 0F 10 40 00
  004010F0 68 B4 60 42 00 B9 E8 99 42 00 E8 A1 04 00 00 8B
  00401100 C8 E8 FF FE FF FF EB 43 8B 45 FC 50 68 88 60 42
  00401110 00 E8 6A 25 00 00 83 C4 08 68 0F 10 40 00 68 84
  00401120 60 42 00 8B 4D FC 51 68 60 60 42 00 B9 E8 99 42
  00401130 00 E8 6A 04 00 00 8B C8 E8 33 01 00 00 8B C8 E8
  00401140 5C 04 00 00 8B C8 E8 BA FE FF FF FF 15 BC C2 42
  
  00401040 push ebp
  00401041 mov ebp,esp
  00401043 sub esp,5Ch
  00401046 push ebx
  00401047 push esi
  00401048 push edi
  00401049 push 0
  0040104B call dword ptr [__imp__CoInitialize@4 (0042c2b8)]
  00401051 mov dword ptr [ebp-4],eax
  00401054 cmp dword ptr [ebp-4],0
  00401058 jge main+35h (00401075)
  0040105A push offset @ILT+10(endl) (0040100f)
  0040105F push offset string "CoInitialize failed." (00426114)
  00401064 mov ecx,offset cout (004299e8)
  00401069 call ostream::operator<< (004015a0)
  0040106E mov ecx,eax
  00401070 call @ILT+0(ostream::operator<<) (00401005)
  00401075 lea eax,[ebp-14h]
  00401078 push eax
  00401079 mov ecx,dword ptr [pid (00428d50)]
  0040107F push ecx
  00401080 call dword ptr [__imp__CLSIDFromProgID@8 (0042c2c0)]
  00401086 mov dword ptr [ebp-4],eax
  00401089 cmp dword ptr [ebp-4],0
  0040108D jge main+6Fh (004010af)
  0040108F push offset @ILT+10(endl) (0040100f)
  00401094 push offset string "CLSIDFromProgID failed." (004260f8)
  00401099 mov ecx,offset cout (004299e8)
  0040109E call ostream::operator<< (004015a0)
  004010A3 mov ecx,eax
  004010A5 call @ILT+0(ostream::operator<<) (00401005)
  004010AA jmp main+10Bh (0040114b)
  004010AF push offset @ILT+10(endl) (0040100f)
  004010B4 push offset string "CLSIDFromProgID succeeded." (004260d8)
  

machine language

• The one “true” computer language
  • …except there isn't just one
  • Every computer has its own machine language
• All other computer languages created for human convenience
  • The computer doesn't understand C
  • Must be converted into machine language

computer languages

most languages were designed with one or the other mechanism in mind

• but there are interpreters for C, and there are compilers for BASIC

---

so let's look at the whole process

• write a program
  • text editor
• compile the program
  • C compiler
  • will do one of two things:
    • print error messages and abort
    • produce an executable program
• run the program

---

Development Environment

• Microsoft Visual Studio
  • use MSVC project
  • developing C\C++ using Microsoft Visual C++ 6.0, courtesy of the system dep.English Hebrew
• Command line
  • use Microsoft tools from the command line
  • you need to add the directory where all the tools are to your search path (PATH environment variable)

---

Command line

Example - hellow.c

cl hello.c -o hello hello

---

Convert Fahrenheit to Celsius

#include int main() { float fahr; float celsius; scanf("%f", &fahr); celsius = 5 * (fahr - 32) / 9; printf("Fahrenheit = %.2f, Celsius = %.2f\n", fahr, celsius); }

---

Editors

• Microsoft - MSVC project builtin
• wordpad, notepad - You can use wordpad to create or edit text files that contain formatting or graphics. Use notepad for basic text editing or for creating Web pages.
• emacs - GNU project Emacs
  • the user functionality of GNU Emacs encompasses everything other Emacs editors do, and it is easily extensible since its editing commands are written in Lisp
  • xemacs - a version of emacs
  • .emacs - an initialization file example
• vi - a programmers text editor, available under cygwin.
• Editor of your choice

---

computer numbers

• To the computer, everything is numbers.
• Computers use binary (base 2)
  • each digit is 0 or 1
  • represents a power of 2

---

human numbers

• You are familiar with decimal (base 10)

  dn dn-1 dn-2... d2 d1 d0 =

  dn x 10n + dn-1 x 10n-1 + dn-2 x 10n-2 ... d2 x 102 + d1 x 101 + d0 x 100

  38469 =

  3 x 10 4 + 8 x 10 3 + 4 x 10 2 + 6 x 10 1 + 9 x 10 0

---

binary

• only two possible values for each digit

  bn bn-1 bn-2... b2 b1 b0 =

  bn x 2n + bn-1 x 2n-1 + bn-2 x 2n-2 ... b2 x 22 + b1 x 21 + b0 x 20

  10110110 =

  1 x 2 7 + 0 x 2 6 + 1 x 2 5 + 1 x 2 4 + 0 x 2 3 + 1 x 2 2 + 1 x 2 1 + 0 x 2 0 =

  1 x 128 + 0 x 64 + 1 x 32 + 1 x 16 + 0 x 8 + 1 x 4 + 1 x 2 + 0 x 1 =

  128 + 32 + 16 + 4 + 2 =

  182

---

Other numbering systems

• octal – base 8
  • used rarely, but you should at least recognize it
  • digits are 0 through 7

  on on-1 on-2... o2 o1 o0 =

  on x 8n + on-1 x 8n-1 + on-2 x 8n-2 ... o2 x 82 + o1 x 81 + o0 x 80

  3264 =

  3 x 8 3 + 2 x 8 2 + 6 x 8 1 + 4 x 8 0 =

  3 x 512 + 2 x 64 + 6 x 8 + 4 x 1 =

  1536 + 128 + 48 + 4 =

  1716

• hexadecimal – base 16
  • used occasionally – you can't really avoid it
  • digits are 0-9, a-f

  hn hn-1 hn-2... h2 h1 h0 =

  hn x 16n + hn-1 x 16n-1 + hn-2 x 16n-2 ... h2 x 162 + h1 x 161 + h0 x 160

  3b7e =

  3 x 16 3 + 11 x 16 2 + 7 x 16 1 + 14 x 16 0 =

  3 x 4096 + 11 x 256 + 7 x 16 + 14 x 1 =

  12288 + 2816 + 112 + 14 =

  15230

---

Converting from one base to another

• The computer works in base 2
• Some times it is convenient to represent numbers in hex

Number: Radix: Number:

---

Maintained by Efi Fogel. Last modified: February 15 2004.