Computer Programming I

Today’s Lecture  Components of a computer  Program  Programming language  Binary representation

Copyright © 2006 Pearson Addison-Wesley. All rights reserved. 1-3 Computer Components  Hardware  CPU  IO device  Main memory  Software  How does computer work?

Computer Components

The Central Processing Unit  “brain” of the computer.

Memory  Random Access Memory (RAM)  Temporary memory  Main memory  Read Only Memory (ROM)  For start-up directions  permanent memory.

The execution speed of a program depends on  CPU  RAM  Why?

Programs  Computer  Hardware  Software  Programs that run on a computer  Operating system  Application software

Copyright © 2006 Pearson Addison-Wesley. All rights reserved. 1-9 Programming Languages  Three types of programming languages 1. Machine languages  Strings of numbers giving machine specific instructions  Example:

Copyright © 2006 Pearson Addison-Wesley. All rights reserved Programming Languages  Three types of programming languages 2. Assembly languages  English-like abbreviations representing elementary computer operations (translated via assemblers)  Example: LOAD BASEPAY ADD OVERPAY STORE GROSSPAY

Copyright © 2006 Pearson Addison-Wesley. All rights reserved Programming Languages  Three types of programming languages 3. High-level languages  Codes similar to everyday English  Use mathematical notations (translated via compilers)  Example: grossPay = basePay + overTimePay

Copyright © 2006 Pearson Addison-Wesley. All rights reserved Programming Languages (3) Machine Languages Assembly Languages High-Level Languages LOAD A ADD B STORE C C=A+B

Copyright © 2006 Pearson Addison-Wesley. All rights reserved C++  C++ is a third generation language  Why C++ not C  C++ is an object oriented language

Decimal System  Positional base 10 numeral systems  10 digits: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9  Use same symbol for different orders of magnitude  For example, “1262” in base 10  1* * * *10 0

Binary  A computer is a “bistable” device  A bistable device:  Easy to design and build  Has 2 states: 0 and 1  One Binary digit (bit) represents 2 possible states (0, 1)

Bits  With 2 bits, 4 states are possible (2 2 = 4) Bit 1 Bit 0 State

Decimal to Binary representation  0: 0  1: 1  2: 10  3: 11  4: 100  5: 101  6: 110  7: 111  8: 1000  9: 1001  10: 1010  11: 1011  12: 1100  13: 1101  14: 1110  15: 1111  16:  17: 10001

Convert Binary to Decimal 18  Interpret binary numbers (transform to base 10)  1101 = 1*2 3 +1*2 2 +0*2 1 +1*2 0 = =13  Translate the following binary number to decimal number 

Convert Decimal to Binary  Procedure: 1. Divide the decimal number by 2 2. Make the remainder the next digit to the left of the answer 3. Replace the decimal number with the quotient 4. If quotient is not zero, Repeat 1-4; otherwise, done

Algorithm  A finite set of well-defined instructions for accomplishing some task which, given an initial state, will terminate in a corresponding recognizable end-state.  Examples:  Select the largest number from a set of number (n)  Suppose n numbers are a1, a2, …an  Set LG=a1;  For i=2 to n, do  if LG<ai, then set LG=ai;  Else do nothing;  The largest number is LG

Convert Decimal number 100 to Binary Number 100 % 2 = 0=> last digit 100 / 2 = % 2 = 0=> 2 nd last digit 50/2 = % 2 = 1=> 3rd last digit 25 / 2 = % 2 = 0=> 4th last digit 12 / 2 = 6 6 % 2 = 0 => 5 th last digit 6 / 2 = 3 3 % 2 = 1 => 6 th last digit 3 / 2 =1 1 % 2 = 1 => 7 th last digit 1 / 2 = 0 The result is

Convert Decimal Number 1492 to Binary Number

Bytes and Words  A group of 8 bits is a byte  A byte can represent 2 8 = 256 possible states  Several bytes grouped together to form a word  Word length of a computer, e.g., 32 bits computer, 64 bits computer

Memory Size Metrics  1KB = 1024 bytes  1MB = 1024 x 1024 bytes  1GB = 1024 x 1024 x 1024 bytes

Representing Text  Text is a series of characters  letters, punctuation marks, digits 0, 1, …9, spaces, return (change a line),…  How many bits do we need to represent a character?  1 bit can be used to represent 2 different things  2 bit … 2*2 = 2 2 different things  n bit 2 n different things  In order to represent 128 different character  Solve 2 n = 128 for n  n=7

ASCII  The American Standard Code for Information Interchange  128 characters  7 bits could be used to represent ASCII characters  However, in 1960s, an 8-bit byte was becoming hardware standard, therefore, it was decided to use 1 byte (8 bits) to store the ASCII code (first 7 bits), with the eighth bit being used as a parity bit to detect transmission errors

ASCII Table