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Lecture 4
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Lecture 4

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basics of computers

basics of computers

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  • 1. Flow Charts
  • 2. Flow Charts •A diagrammatic representation that illustrates the sequence of operations to be performed to get the solution of a problem. • Generally drawn in the early stages of formulating computer solutions. • Facilitate communication between programmers and business people. • Play a vital role in the programming of a problem and are quite helpful in understanding the logic of complicated and lengthy problems. • Once the flowchart is drawn, it becomes easy to write the program in any high level language. • Must for the better documentation of a complex program.
  • 3. Flow Charts A flow chart can be used to: • Define and analyse processes. • Build a step-by-step picture of the process for analysis, discussion, or communication. • Define, standardise or find areas for improvement in a process.
  • 4. Flow Charts Symbols for drawing a flowchart: Start or End of the program
  • 5. Flow Charts Symbols for drawing a flowchart: Computational Steps or Processing Function of a program
  • 6. Flow Charts Symbols for drawing a flowchart: Input or output operation
  • 7. Flow Charts Symbols for drawing a flowchart: Decision Making and Branching
  • 8. Flow Charts Symbols for drawing a flowchart: Connector or joining of two parts of program
  • 9. Flow Charts Symbols for drawing a flowchart: Magnetic Tape
  • 10. Flow Charts Symbols for drawing a flowchart: Magnetic Disk
  • 11. Flow Charts Symbols for drawing a flowchart: Off-page connector
  • 12. Flow Charts Symbols for drawing a flowchart: Flow lines
  • 13. Flow Charts Symbols for drawing a flowchart: Annotation (foot note)
  • 14. Flow Charts Symbols for drawing a flowchart: Display
  • 15. Flow Charts Guidelines in flowcharting - • In drawing a proper flowchart, all necessary requirements should be listed out in logical order. • The flowchart should be clear, neat and easy to follow. There should not be any room for ambiguity in understanding the flowchart. • The usual direction of the flow of a procedure or system is from left to right or top to bottom.
  • 16. Flow Charts …Guidelines in flowcharting - • Only one flow line should come out from a process symbol. OR
  • 17. Flow Charts …Guidelines in flowcharting - • Only one flow line should enter a decision symbol, but two or three flow lines, one for each possible answer, should leave the decision symbol.
  • 18. Flow Charts …Guidelines in flowcharting – Only one flow line is used in conjunction with terminal symbol.
  • 19. Flow Charts …Guidelines in flowcharting – Write within standard symbols briefly. As necessary, you can use the annotation symbol to describe data or computational steps more clearly. This is confidential data
  • 20. Flow Charts …Guidelines in flowcharting – • In case of complex flowchart, it is better to use connector symbols to reduce the number of flow lines. Avoid the intersection of flow lines. • Ensure that the flowchart has a logical start and finish. • It is useful to test the validity of the flowchart by passing through it with a simple test data.
  • 21. Flow Charts Advantages Of Using Flowcharts : • Effective communication • Effective analysis • Proper documentation • Efficient Coding • Proper Debugging • Efficient Program Maintenance
  • 22. Flow Charts Limitations of using Flowcharts : • Complex logic: Sometimes, the program logic is quite complicated. • Alterations and Modifications: Alterations may require re-drawing completely. • Reproduction: As the flowchart symbols cannot be typed, reproduction of flowchart becomes a problem.
  • 23. Flow Charts Example 1. Draw a flowchart to find the sum of first 50 natural numbers.
  • 24. Flow Charts Example 2 Draw a flowchart to find the largest of three numbers A,B and C.
  • 25. Flow Charts Example 3 Draw a flowchart for computing factorial of a given number
  • 26. Assignment Fill in the blanks- 2. A program flowchart indicates the_________ to be performed and the __________ in which they occur. 3. A program flowchart is generally read from _____________ to ________________ 4. Flowcharting symbols are connected together by means of ___________________ 5. A decision symbol may be used in determining the ____________ or ___________ of two data items. 6. __________ are used to join remote portions of a flowchart 7. ____________ connectors are used when a flowchart ends on one page and begins again on other page 8. A ________ symbol is used at the beginning and end of a flowchart. 9. The flowchart is one of the best ways of ________ a program.. 10. To construct a flowchart, one must adhere to prescribed symbols provided by the __________ . 11. The program uses a ____________ to aid it in drawing flowchart symbols.
  • 27. Answers • Operations, sequence • Top, down • Flow line • Equality, inequality • connectors • Off -page • Terminal • documenting • ANSI (American National Standards Institute) • Flowcharting template
  • 28. Structured English
  • 29. Structured English • Structured English is a tool used to represent process logic. • Syntax rules are not very strict & an English statement is used to specify an action. • The main aim is to allow easy readability, which helps in documentation. Two building blocks of Structured English: 6. Structured logic or instructions organized into nested or grouped procedures 7. Simple English statements such as add, multiply, move
  • 30. Structured English Four conventions to follow when using Structured English: • Express all logic in terms of sequential structures, decision structures, or iterations. • Use upper case for keywords such as: IF, THEN, ELSE, DO, DO WHILE, DO UNTIL, PERFORM • Indent blocks of statements to show their hierarchy (nesting) clearly. • When words or phrases have been defined, underline those words or phrases to indicate that they have a specialised, reserved meaning.
  • 31. The Flow of Structured English Plain Structured Pseudocode Programs English English User Analyst Programmer
  • 32. …Structured English The conventions are used in writing structured English: • Imperative Sentences: Store the data in database. • Arithmetic & Relational Operations : Common symbols of mathematics are used in structured English such as- + for add, - for subtraction etc. and =, >=, != etc. are used for relational operations.
  • 33. …Structured English 3. Decision Structures: If Then Else, Select Case 4. Repetion: Loops There are various forms in which structured english can be implemented to solve the problem. e.g. Algorithm, Flowchart, pseudocode.
  • 34. …Structured English
  • 35. Writing Structured English Repetition Conditions IF … THEN … DO statements … statements … ELSE UNTIL end-condition statements … END IF or or SELECT CASE 1 (conditions) DO WHILE statements … statements … CASE 2 … END DO statements … END SELECT
  • 36. Pseudocode
  • 37. Pseudocode • An outline of a program, written in a form that can easily be converted into real programming statements. • Pseudocode cannot be compiled nor executed, and there are no real formatting or syntax rules.
  • 38. …Pseudocode • It enables the programmer to concentrate on the algorithms without worrying about all the syntactic details of a particular programming language. • Flowcharts can be thought of as a graphical form of pseudocode.
  • 39. Example of Pseudocode Regular code (written in PHP): <?php if (is_valid($cc_number)) { execute_transaction($cc_number, $order); } else { show_failure(); } ?> Pseudocode: if credit card number is valid execute transaction based on number and order else show a generic failure message end if