Program Design (Copy)

1. Introduction to Program Design

• Program design is a crucial phase in software development.
• It involves breaking down a problem into structured components.
• Key tools used in program design include:
  • Structure charts
  • State-transition diagrams
  • Pseudocode

2. Structure Charts

• A structure chart is a modeling tool used to decompose a problem into sub-tasks.
• It visually represents a program’s hierarchy, showing different modules and their interactions.
• Key Features of Structure Charts:
  • Modules are represented by boxes.
  • Arrows indicate the flow of parameters between modules.
  • Each level refines the module above it.
• Example:
  • Converting temperature from Fahrenheit to Celsius.
  • Top-level module: Convert temperature.
  • Sub-modules: Input temperature, Convert to Celsius, Output temperature.
• Selection in Structure Charts:
  • Decision-making represented using a diamond-shaped box.
  • Example: Converting between Fahrenheit and Celsius based on user input.
• Repetition in Structure Charts:
  • Uses a semi-circular arrow to indicate loop conditions.
  • Example: Repeating conversion until user enters a specific termination value (e.g., 999).

3. State-Transition Diagrams

• A Finite State Machine (FSM) is a model that represents a system in a specific state, transitioning between states based on inputs.
• Components of FSM:
  • States: Represented as circles.
  • Transitions: Indicated by arrows between states.
  • Events: Labels on arrows specifying triggering conditions.
  • Conditions: Written in square brackets next to an event label.
  • Initial state: Marked with an arrow having a black dot.
  • Final state: Indicated using a double circle.
• Use Cases of FSM in Program Design:
  • Controlling user input validation.
  • Managing multi-step processes (e.g., ATM operations, vending machines).
  • Simulating real-world processes (e.g., traffic lights, game AI behavior).

4. Deriving Pseudocode from Structure Charts

• Step 1: Create an Identifier Table
  • Lists variables, constants, and their descriptions.
  • Example:
    • radius: Stores user input for radius.
    • answer: Stores calculated value.
    • pi: Constant set to 3.142.
• Step 2: Declare Constants and Variables in Pseudocode

  DECLARE radius : REAL
  DECLARE answer : REAL
  CONSTANT pi ← 3.142
  

• Step 3: Define Functions for Calculations

  FUNCTION calculateVolume(radius: REAL) RETURNS REAL
      RETURN (4 / 3) * pi * radius * radius * radius
  ENDFUNCTION 
  
  FUNCTION calculateSurfaceArea(radius: REAL) RETURNS REAL
      RETURN 4 * pi * radius * radius
  ENDFUNCTION
  

• Step 4: Define Procedures for Input and Output

  PROCEDURE inputRadius
      OUTPUT "Please enter the radius of the sphere"
      INPUT radius
      WHILE radius < 0 DO
          OUTPUT "Please enter a positive number"
          INPUT radius
      ENDWHILE
  ENDPROCEDURE
  
  PROCEDURE outputAnswer
      OUTPUT answer
  ENDPROCEDURE
  

• Step 5: Main Algorithm with Selection and Repetition

  CALL inputRadius
  WHILE radius <> 0
      OUTPUT "Do you want to calculate the Volume (V) or Surface Area (S)"
      INPUT reply
      IF reply = "V"
          THEN answer ← calculateVolume(radius)
          OUTPUT "Volume: ", answer
      ELSE
          answer ← calculateSurfaceArea(radius)
          OUTPUT "Surface Area: ", answer
      ENDIF
      CALL outputAnswer
      CALL inputRadius
  ENDWHILE
  

5. Activities for Practicing Program Design

• Activity 12A: Draw a structure chart to input height and width of a triangle, calculate and output its hypotenuse.
• Activity 12B: Modify the structure chart to calculate either the volume or surface area of a sphere.
• Activity 12C: Extend the algorithm to continue execution until a termination condition (e.g., entering 0) is met.
• Activity 12D: Implement a temperature conversion algorithm supporting both Fahrenheit to Celsius and Celsius to Fahrenheit conversions.

6. Summary of Key Concepts

• Structure Charts: Used for hierarchical decomposition of a program.
• State-Transition Diagrams: Used to document FSM behavior in programs.
• Pseudocode: Derived from structure charts for systematic program development.
• Design Principles: Essential for creating structured, modular, and maintainable code.
• Repetition and Selection: Incorporated into both structure charts and pseudocode.