1. Alexandria University Faculty of Science Computer Science Department
 Introduction to Programming (CS 102)

2. The Program Development Life Cycle
Creating new programs is called program development.
Creating successful applications requires planning
Computer professionals need to develop new or modified applications from time to time
The process associated with creating successful applications programs is called the program development life cycle (PDLC).

3. The Program Development Life Cycle

4. 1. Problem Analysis During analysis, a systems analyst and programmer:
review specifications, and
talk with users to fully understand what the software should do.
Documentation consists of:
program specifications,
timetable,
which language will be used,
how the program will be tested, and
what documentation is required.

5. 2. Program Design
Program design: stage where program specifications are expanded into a complete design of the new program.
Structured programming and object-oriented programming are two of the most significant approaches to the design process.

6. Program Design: Program Design Tools
Program design tools are planning tools.
Structure charts
Program flowcharts
Pseudocode
Data modeling

7. Structure Charts Structure charts depict the:
overall organization of a program, and
how the modules of a program are defined and
how they connect to each other hierarchically.
Program modules should be arranged hierarchically  in a top-down fashion
Why?? So that their relationship to each other is apparent.

9. Flowcharts
Use geometric symbols and familiar relational operators to provide a graphic display of the sequence of steps involved in a program
Different symbols are used to represent different actions such as
Start/stop
Decision
Input/output
Processing
Looping symbols

13. Pseudocode
Uses English-like statements in place of the graphic symbols of the flowchart.
Unlike a flowchart, pseudocode is easy to modify and can be embedded into a program as comments.
No standard set of rules exists for writing pseudocode, although a number of conventions have been developed.

15. Program Design: Program Design Tools
Data modeling
is a technique used to illustrate the data in an application and is frequently used with object-oriented programming.
In a data model, the objects in the program are identified, along with their variables and class.

16. Program Design: Good Program Design
n    Good program design is essential; it can save time and it produces a better end result. Some principles of good program design are:
Be specific
One-entry-point, one-exit-point rule
No infinite loops
Documentation during program design includes all the design specifications

18. 3. Program Coding
Coding: actual process of creating the program in a programming language.
Programming language must be chosen.
Coding standards should be adhered to.
Make use of reusable code and data dictionaries.
Translate coded programs into executable code.
Documentation results in finished source code.

20. 3. Program Coding cont’d
The coded program is referred to as source code. To be executed, the program is converted by the computer to object code using a special program.
A compiler translates the entire program into machine language before executing it. The program then doesn’t need to be recompiled until it is modified.
An interpreter translates program statements one at a time. Interpreters are helpful during the debugging stage, but are slower during execution of the finished program.
An assembler converts assembly-language statements into machine language.

22. 4. Program Debugging and Testing
Debugging: process of making sure a program is free of errors or bugs.
Preliminary bugging often finds syntax or logic errors.
Testing can consist of alpha or beta testing.
Documentation includes a copy of the finished program code, plus test data and results.

23. 4. Program Debugging and Testing cont’d
Preliminary debugging begins after the program has been entered into the computer system.
Rarely is a program error-free the first time it runs.
Two common types of errors are syntax errors and logic errors:
A syntax error occurs when the programmer has not followed the rules of the language.
A logic error, or execution-time error, results when the command syntax is correct but the program is producing incorrect results.

24. 5. Program Maintenance
Program maintenance: process of updating software so that it continues to be useful.
A costly process, but can be used to extend the life of a program.
Documentation consists of amended program package reflecting what problems occurred and what program changes were made.

25. What Is a Programming Language?
A programming language is a set of rules used to write instructions to the computer.

26. Categories of Programming Languages
Low-level languages
High-level languages
Fourth-generation languages (4GLs)
Natural and visual languages

27. Machine and Assembly Languages
Machine and assembly languages are called low-level languages
Programmers who code in them must write instructions at the finest level of detail, the base level of the hardware
Virtually no one writes machine-language programs anymore
All programs must be translated by a language translator into machine language before they are executed
Assembly languages are fast and consume little storage when compared with higher-level languages, but take longer to write and maintain

28. High-Level Languages
· High-level languages differ from their low-level predecessors in that they require less coding detail and make programs easier to write.
Programs written in a high-level language (BASIC, COBOL, Pascal, C, etc.) need to be translated into machine language before they can be executed.

29. Fourth Generation Languages (4GL)
Very-high-level languages that are much easier to use than the high-level languages
They are declarative rather than procedural languages.
For instance, to draw a bar chart in a procedural language, you must tell the computer how to draw bars and where to place them.
In a declarative language, you may be able to just point to the data you want graphed, click several menu choices, and you’re in business.
Fourth-generation languages are commonly used to access databases (query languages).

30. Popular Programming Languages
FORTRAN
COBOL
Pascal
BASIC and Visual Basic
C, C++, AND C#
Java

32. Markup Languages
Markup languages use symbols or tags to describe what a document should look like when displayed.
HTML (Hypertext Markup Language)
Dynamic HTML
XML (extensible markup language)
XHTML (extensible Hypertext Markup Language)
WML (Wireless Markup Language )

34. Scripting Languages
Scripting languages are used to build program instructions into Web pages, usually to add dynamic content.
JavaScript
VBScript
Perl

36. Flowcharts
Understanding the basic parts of the flowchart and the advantages and limitations of flowcharts.

37. Definition
Flowcharts  a diagrammatic representation that illustrates the sequence of operations to be performed to get the solution of a problem.

38. How to Write a Program? Start Define Problem to Solve
Think of an Algorithm
Think of a Technique for the Solution
Write Solution on a Piece of Paper
If not Finished Repeat Steps 4 and 5
Write Code and Program
Debug and Test
If not Finished Repeat Steps 7 and 8
Stop

39. How to Write a Program? Start Job Done No Define Problem to Solve
Think of an Algorithm
(Technique for the solution)
Yes
Write Code and Program
Idea!!!!
Debug and Test
Think of a
Technique for the solution
Job Done No
Yes
Stop
Write it down
on a piece of paper
(before you forget it!!!)

40. Algorithms A computer program makes use of algorithms
Algorithm  is a complete step-by-step procedure for solving a problem or accomplishing a task.

41. Standard Flowchart Symbols
Start Or Stop Process
Start
Print
Results
Input/Output A
On-Page Connector ?
Yes No
Condition
Calculate
Variables
Process Rectangle A1
Off-page Connector

42. Example of Flow Charts

43. Basic Flow Chart Operations
All computer instructions are based on four basic processing patterns:
Simple Sequence
Selection Pattern
Loop Pattern
Branch Pattern

44. Simple Sequence
Logic involves executing instructions one statement after another, in the order presented by the program.
This is the simplest and most-used pattern.
The computer assumes that all instructions are to be executed in this order unless the program presents other instructions.

45. Example of a Simple Sequence
Read Names
Compare with Criteria
Print Eligible Names

46. Selection Pattern
Requires that the computer make a choice among two or more items.
Each choice is based on one of two comparisons a computer can make: true or false (Yes or No).

47. Example of a Selection Pattern?
Honour Student No
Yes
List under
Student Loan
List under
Scholarships

48. Loop Pattern
Causes an interruption in the normal sequence of processing and directs the computer to loop back to a previous statement in the program, repeating the same sequence over again, usually with new data.
By looping, the programmer avoids having to repeat the same set of instructions over and over.

49. Example of a Loop Pattern?
More Names No
Yes
Compare with Criteria
Print Eligible Names

50. Branch Pattern Is often used in combination with selection or looping.
The branch pattern allows the computer to skip statements in a program.
The branch encourages undisciplined jumping around among program statements, a characteristic that is frowned on by most programming experts.
Branching is difficult to follow and is an inefficient use of computer power.

51. Example of a Branch Pattern?
Honour Student No 1
Yes
Read Area of Concentration
Read Courses Taken 1
Compare with Criteria

52. Types of Flowcharts Functional Chart Process Flow Chart
A chart that is used to describe how activities interact with one another within an organization as well as with other organization and/or systems.
Process Flow Chart
A chart that is used to describe the sequence and relationship of the tasks that make up an activity
3. Process Flow Description Chart
Detailed description of the tasks outlined in a Process Flow Chart
Typically used to show the kinds of tasks performed within a process (the number of operations, review, and transfers; and the amount of storage and time required to complete an activity)

53. Uses of Flowcharts
Flowcharts are generally drawn in the early stages of formulating computer solutions.
Flowcharts facilitate communication between programmers and business people.
Flowcharts 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.
Often we see how flowcharts are helpful in explaining the program to others.
Hence, it is correct to say that a flowchart is a must for the better documentation of a complex program.

54. Advantages of Flowcharts
Communication: Flowcharts are better way of communicating the logic of a system to all concerned.
Effective Analysis: With the help of flowchart, problem can be analysed in more effective way.
Proper Documentation: Program flowcharts serve as a good program documentation, which is needed for various purposes.

55. Disadvantages of Flowcharts
Complex Logic: Sometimes, the program logic is quite complicated. In that case, flowchart becomes complex and clumsy.
Alterations and Modifications: If alterations are required the flowchart may require re-drawing completely.
Reproduction: As the flowchart symbols cannot be typed, reproduction of flowchart becomes a problem.
The Essentials of what Is Done can easily be lost in the technical details of how it is done

56. Case Study - 1
A certain Company gives each of its sales people $1,000 at the beginning of each month to cover travel, lodging, and food expenses. At the end of the month, a salesperson must total his/her expense receipts. If the amount is less than $1,000 then the difference must be returned to the company.

57. Case Study – 1 (Solution)
Here is an algorithm for figuring how much money, if any, must be returned:
Total the expense receipts for the month.
2. Subtract the amount of the expense receipts from 1,000.
3. If the remainder is more than 0, return that amount to the company.

58. Flowchart Start Input Expenses ? E<1000 Yes Subtract Expenses
R <= 1000-E No
Print
You Owe $0
Print
You Owe $R
Stop

59. Case Study – 1 (Solution 1)
Assume the Employee has Spent $1250
What would be the amount to return to the company in this case?

60. Solution 1 E = $1250 Start Input Expenses ? E<1000 Yes
Subtract Expenses
R <= 1000-E No
Print
You Owe $0
Print
You Owe $R
Stop

61. Case Study – 1 (Solution 2)
Now Assume the Employee has spent $950
What would be the amount to return to the company in this case?

62. Solution 2 E = $950 R = 1000 - E E = $50 Start Input Expenses ?
Yes
R = E
Subtract Expenses
R = 1000-E No
E = $50
Print
You Owe $0
Print
You Owe $R
Stop

63. Basic Guidelines for Flowcharts
Only one flow line should come out from a process symbol.

64. Basic Guidelines for Flowcharts
< = ?
>
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.               Y N ?

65. Basic Guidelines for Flowcharts
Only one flow line is used in conjunction with terminal symbol.                 
Start
Stop

66. Basic Guidelines for Flowcharts
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.

67. Case Study - 2
Draw a flowchart to find the sum of first 5 natural numbers.

68. Case Study - 2 N Sum 1 1 2 3 3 6 4 10 5 15 Start Sum = 0 N = 0
N = N + 1 1 1
Sum = Sum + N 2 3 ?
N = 5 3 6 No 4 10
Yes 5 15
Print Sum
Stop

69. Case Study - 3
Draw a flowchart to find the largest of three numbers A,B, and C.

70. Case Study - 3 Start Read A, B, C ? B > C ? A > B ? A > C YesNo
Yes
Yes No No
Print B
Print C
Print C
Print A
Stop

71. Case Study – 3 - (Solutions)
Consider four input cases:
A = ; B = ; C = 3
A = ; B = 3 ; C = 7
A = ; B = ; C = 3

72. Case Study – 3 (Solution 1)
Start
B = 7
Read A, B, C
C = 3 ?
B > C ?
A > B ?
A > C
Yes No
Yes
Yes No No
Print B
Print C
Print C
Print A
Stop

73. Case Study – 3 (Solution 2)
Start
B = 3
Read A, B, C
C = 7 ?
B > C ?
A > B ?
A > C
Yes No
Yes
Yes No No
Print B
Print C
Print C
Print A
Stop

74. Case Study – 3 (Solution 3)
Start
B = 3
Read A, B, C
C = 3 ?
B > C ?
A > B ?
A > C
Yes No
Yes
Yes No No
Print B
Print C
Print C
Print A
Stop