CS Data Structures I Chapter 2 Principles of Programming & Software Engineering

2 Topics Software Life Cycle

3 Introduction How do you write a Java program? Old fashion way Write code Compile Check syntax Run Check logic How long will this take? Which phase takes more time?

4 Introduction A better way Systematic way (Structured approach) Specify problem Analyze Design Implement Test Maintain

5 Introduction SW Engineering: Computer science branch that provides techniques for development of computer programs Systematic approach to analyze, design, implement, and maintain software Uses CASE tools

6 The Software Life Cycle 1. Specification 2. Design 3. Risk Analysis 4. Verification 5. Coding 6. Testing 7. Refining 8. Production 9. Maintainence

7 1. Specification & Analysis Specification A contract between the module and any other module using it Doesn't include information about how the task is to be performed or the method of solution, but what May involve construction of a prototype program to get more details from users.

8 1. Specification & Analysis Example: “begin & write a software to store a library’s catalogue of books” Input: Librians enter new books as they arrive Library users enter search keys to search through our list

9 1. Specification & Analysis Process: Add new book Search for books Output: Show all the info about a book Requirements What type of processing is required Are there any time/space/performance constraints

10 2. Design Given: Clear & detailed specification of all aspects of the problem Output: Design for a solution to the problem Idea: Use modular design Divide & conquer Divide the problem into smaller manageable parts.

11 2. Design Generate an outline of the problem solution. Requires breaking the entire problem down into small manageable parts - modules. Modules are self-contained units of code.

12 2. Design Design Example: Sort Function Purpose: Sort an array of integers Specification: Receive an array of N integers (input), where N > 0 (assumption) Return the array (output) with the integers sorted (action) Remember: Specification is a contract

13 2. Design Design Example: Sort Function First-draft specification: Sort(A, N) // Sorts an array // Precondition: A is an array of N integers; N > 0 // Postcondition:Integers in A are sorted What is missing?

14 2. Design Design Example: Sort Function Revised Specification: Sort(A, N) // Sorts an array of MAX_ARRAY elements // Precondition: // A is an array of N integers; // and 1 <= N <= MAX_ARRAY, // where MAX_ARRAY is a global constant // that specifies the maximum size of A // Postcondition: // A [0] <= A [1] <=... <= A [N-1], // N is unchanged

15 3. Risk Analysis Risks are primarily business related but can be personal as well. Example: If a piece of software is not ready in time the company may lose the market to a competitor. Not an important issue for this course.

16 4. Verification Determining the degree to which a software product fulfills its specification Formal, theoretical methods for proving algorithm correctness Assertion (Predicate): Statement about a particular condition at certain point in an algorithm Invariant: Condition that is always true at a certain point in an algorithm

17 5. Implementation (Coding) Coding Translating the algorithm into a particular programming language & removing syntax errors Should not start unless previous stages are well defined Original solution usually simplified

18 5. Coding Bottom-up implementation: First implement submodules, then modules Top-down implementation: Implement a module before implementing its submodules Use stubs Refinement might be needed Stubs: Dummy functions that do nothing and are placed in the place of submodules to focus attention on the module itself A S3S2S1

19 6. Testing Careful design of test data is important Valid (In-range) data Invalid (out-of-range) data Random values of data Test several times on different circumstances Any modification in the program needs re- testing

20 7. Refining the Solution Usually involves increasing the "robustness" of a solution. Often simplifying assumptions are made in the design process that must be removed from final versions. Example: assume that the input will be be integers between 0 and During this step code would be inserted to actually test the input values.

21 8. Production Distribute the SW product to its intended users Install the SW Use the SW

22 9. Maintenance Correct errors not discovered during testing Add more features Enhance existing features Modify to suit the user better

23 Review The first phase of the life cycle of software is the ______ phase. design risk analysis specification coding

24 Review The syntax errors of a program are removed during the ______ phase of the program’s life cycle. verification coding testing refining maintenance

25 Review Which of the following is an example of a logical error? an algorithm that calculates the monthly payment of a loan displays incorrect results an array subscript in a program goes out of range a program expects a nonnegative number but reads –23 the beginning of a while loop is written as “whille” instead of “while”

26 Review During the design phase of the software life cycle, the program is divided into ______. invariants loops Modules prototypes

27 Review A prototype program is created during the ______ phase of the software life cycle. design specification Coding testing