1. Lecture #1: Introduction to Algorithms and Problem Solving Dr. Hmood Al-Dossari King Saud University Department of Computer Science 6 February 2012

2. Overview  Data and Information  Computer Operations  Problem Solving Steps  Programs and Programming  Types of Computer Languages  Levels of Computer Languages  Programming and Problem Solving  Algorithms

3. Data and Information  Data are raw facts : e.g. transactions, dates and amounts.  Information are data that have been processed into a usable form: e.g. tables, documents, and charts.  Goal of computer applications is to process data into information

4. Data and Information  Calculate the total amount of purchasing a video game with tax. Output (Information) Processing Input (Data) Taxes amount due Tax= Price x Percentage Total amount = Price + Tax Video game price Tax Percentage 1070Tax= 1000 x 0.07 Total amount = 1000 + 70 Price = 1000 Percentage = 7%

5. Computer Operations  There are six basic computer operations: 1. Receive data (input). 2. Store data in memory. 3. Perform arithmetic and logic operations. 4. Make Decisions. 5. Repeat a group of operations. 6. Output the processed data (information).

6. Computer Operations

7. Program and Programming  Program is a collection of instructions that tell the computer what to do.  It is generically known as "software”.  The process of creating a program is called programming.  A program is written in a programming language, such as C, C++ or Java.

8. Program and Programming  The computer only knows what it is told through programs, so they must be accurate and very specific.  The instructions are written by the programmer.  The instructions are converted into the computer's machine language by software called "compilers“.

9. Types of Computer Languages Procedural: Monolithic programs that run from start to finish with no intervention from user other than input Basic, QBasic, QuickBasic COBOL FORTRAN C Object Oriented/Event Driven (OOED): Programs that use objects which respond to events; use small segments to code for each object Visual Basic Visual C++

10. Levels of Computer Languages Low Level: at the level of the computer, i.e., in binary (0-1) format Computer can only execute a binary form of a program Intermediate Level: close to the computer but uses English words, e.g., Assembler, that is converted directly into binary High Level: at the level of the programmer using English words and clearly defined syntax; must be converted or translated into binary for computer to implement it, e.g., Visual C++. Need a software program to handle the conversion of high-level into binary

11. Translating from High-level Language to Binary Interpreted: each statement translated as it is executed-- slow but easy to use Compiled: entire program is converted to binary--executes faster, but more difficult to use (.exe files are compiled programs)

12. Translating from High-level Language to Binary

13. Programming and Problem Solving Steps  Programming is a process of problem solving  Problem solving techniques Analyze the problem Outline the problem requirements Design steps (algorithm) to solve the problem  Algorithm: Step-by-step problem-solving process

14. Problem Solving Process  Step 1 - Analyze the problem Outline the problem and its requirements Design steps (algorithm) to solve the problem  Step 2 - Implement the algorithm Implement the algorithm in code Verify that the algorithm works  Step 3 - Maintenance Use and modify the program if the problem domain changes

15. Analyze The Problem  Thoroughly understand the problem  Understand problem requirements : Does program require user interaction? Does program manipulate data? What is the output?  If the problem is complex, divide it into subproblems Analyze each subproblem as above

16. What is an algorithm?  The idea behind the computer program  Stays the same independent of Which kind of hardware it is running on Which programming language it is written in  Solves a well-specified problem in a general way  Is specified by Describing the set of instances (input) it must work on Describing the desired properties of the output

17. What is an algorithm? (Cont’d)  Before a computer can perform a task, it must have an algorithm that tells it what to do.  An algorithm is an ordered set of unambiguous executable steps, defining a terminating process.” Ordered set of steps: structure! Executable steps: doable! Unambiguous steps: follow the directions! Terminating: must have an end!

18. Important Properties of Algorithms  Correct always returns the desired output for all legal instances of the problem.  Unambiguous  Precise  Efficient Can be measured in terms of  Time  Space Time tends to be more important

19. Representation of Algorithms  A single algorithm can be represented in many ways: Formulas: F = (9/5)C + 32 Words: Multiply the Celsius by 9/5 and add 32. Flow Charts. Pseudo-code.  In each case, the algorithm stays the same; the implementation differs!

20. Representation of Algorithms (Cont’d)  A program is a representation of an algorithm designed for computer applications.  Process: Activity of executing a program, or execute the algorithm represented by the program

21. Expressing Algorithms  English description  Flow Chart  Pseudo-code  High-level programming language  More precise  More easily expressed

22. End