Steps in Program Design and Development Lifecycle

Phase 2: Algorithm Development

An algorithm is a set of detailed, unambiguous, and ordered instructions used to produce a desired output from a given input. You can think of an algorithm as a recipe: it must be lucid (understandable), precise, and it must eventually end.

To represent an algorithm before writing actual code, programmers use two primary tools:

• Flowcharts: Visual diagrams that show the flow of logic.
• Pseudocode: A way of writing algorithms using simple English that mimics the structure of a programming language.

When writing pseudocode, it is essential to use indentation. Indentation is not just for neatness; it is used to signify different control structures, making it clear which instructions belong inside a loop or a conditional statement.

Exam Tip: When writing pseudocode, remember that there is no single "standard" format, but you should always use one instruction per line and use keywords to signify logic.

Phase 3: Testing and Desk Checking

Before a single line of code is written, the algorithm must be tested for correctness. This is often done through a process called desk checking.

During desk checking, the programmer "walks through" the logic of the algorithm manually, exactly as a computer would. You use test data and a sheet of paper to keep track of all major variables, ensuring that the instructions actually produce the expected results. This allows you to identify and fix major logic errors early, when they are much easier to correct than once they are embedded in complex code.

Phase 4: Coding and Execution

Only after the design and testing phases are complete should you begin coding the algorithm into a specific programming language.

Once the code is written, the next step is running the program on a computer. This involves using a compiler and programmer-designed test data to check for two types of errors:

1. Syntax Errors: Mistakes in the "grammar" of the programming language.
2. Logic Errors: Mistakes in the reasoning that cause the program to produce the wrong result even if it runs without crashing.

Phase 5: Documentation and Maintenance

The final stage of the lifecycle involves two ongoing activities: documentation and maintenance.

Documentation is split into two types:

• External Documentation: Includes hierarchy charts, the solution algorithm, and test data results.
• Internal Documentation: Comments and notes written directly within the program code.

Program Maintenance refers to the necessary changes made to a program throughout its life, such as fixing new bugs or updating the software to work with new hardware or requirements.

Summary Table: Data Types and Structures