Introduction to programming Carl Smith National Certificate Year 2 – Unit 4 Unit objectives Apply simple analysis and design techniques to the software development process. Develop basic high-level code using an appropriate procedural programming language. Use suitable testing methods to ascertain the correctness of a working piece of code. Produce appropriate documentation for a given program application. Programming languages Pascal is one language among others such as:- C, C++, VB, JAVA, COBOL, ADA, BASIC, Fortran… Each has strengths and weaknesses for various tasks, for example COBOL is ideal for data processing Why Pascal? Experts consider Pascal is ideal for students studying computer science courses because:- It forces structure, very “elegant” “Easy” to learn Very powerful Blaise Pascal, 1623-1662 The Pascal language was named after the 17th century mathematician, Blaise Pascal who invented a calculating machine called “the Pascaline” which could add and subtract and worked with eight rotating gears. Tax clerks of the era viewed it as a threat to their jobs and it was never adopted! Program development Analyse Good program development is performed in 4 main steps… Document Write Test (which match the unit objectives - strangely…!) Program development… In fact there are 6 steps:- 1. Analyse the problem } 2. Develop algorithm 3. Write code Step 2 4. Run the program 5. Test the results 6. Document the program Analysis Phase Analysis is not a trivial task Before you can code you need to know exactly what you are to do You need a clear and precise statement of what is to be done You need to understand what data is available and what is to be assumed You need to know what output is desired and the form it should take Development (Develop/Write/Run) Phase Develop an Algorithm, which is:- “A finite sequence of effective statements that when applied to a problem, will solve it” Write code for the program when the algorithm solves the problem (Compile) and Run the program:- At this point you may discover typing or logic errors!... Testing phase Test that the results are correct and in the form you like Prove that your program produces the correct solution in all cases:- e.g. with arithmetic operations this may mean checking with a calculator or even pencil and paper! After this phase you may need to go back to the development or even analysis phases so the whole process becomes a “cycle” Documentation phase It is very important to fully document a working program He writer knows how the program works (hopefully!) but if others are to modify it they must know the logic used Documentation can also be included in the development phase as remarks within the pseudo and actual code Developing Algorithms Algorithms for solving problems can be developed by:- Stating the problem Dividing the problem into major sub-tasks Dividing each sub-task into smaller tasks Repeating the process until each task is easily solved This is known as “Top Down” design Software “Life-Cycle” Analysis Design Coding Testing/Verification Maintenance Obsolescence What is programming? Giving the computer a logical set of instructions to perform a specific task That is, taking the design algorithm and converting it to code that the computer “understands” Compiled v Interpreted Languages either run “Interpreted” that is each line of code is interpreted into pseudo machine code (binary) at run time Or Compiled, which is the whole program is compiled, prior to running it, into pseudo machine code Interpreted languages tend to be slower in execution but are easier to develop and debug because the interpreter is available to pin point errors at run time Pascal is a compiled language but the compiler is part of the “Turbo Pascal” development environment Turbo Pascal 7 MSDOS based environment Therefore 8.3 filenames Support for the mouse but mainly used via the keyboard Runs in a window or full screen under Windows 95/98 or 2000 Turbo Pascal v7 – Main Turbo Pascal v7 - Editor Output name program Program Components Remarks – “Self documenting code” Program Structure Declarations – Variables/Constants & Data Types Input, Output & Formatting Arrays Decisions – “IF” Iteration - Looping} “Nesting” Arithmetic and regular expressions Commands, Procedures and Functions :– In Built and User Defined Pascal - Program Structure Program <name>; } Program Name Uses Crt; - output to screen Const <list of constants> Declaration Var section <list of variables> <list of subprograms> BEGIN END. } Executable section Summary We covered:- National Certificate Unit 4 objectives The software development cycle The software life cycle Intro to Turbo Pascal 7 Program Elements and structure Any Questions?
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