Program Logic and Design: Basic Structures

Introduction

Sequence Structure
- Performs actions in order without branching or skipping.
- Example: Driving directions.
- Actions are performed step by step until the sequence ends.
- Visual: Boxes stacked on top of each other.
Selection Structures (Decision Structures)
- Dual Alternative Ifs (If-Then-Else)
  - Two alternatives (Yes or No).
  - Example: Traffic decisions based on road conditions.
  - Always close an If statement.
- Single Alternative Ifs
  - Only one alternative action if condition is true.
  - Example: Taking an umbrella if it is raining.
  - Null case: No action if condition is false.
- Flowchart and Pseudocode
  - Starts with a decision symbol (diamond shape).
  - Branches (flow lines) join at the bottom.
Loop Structure (Repetition or Iteration)
- Repeats actions while a condition remains true.
- While Loop
  - Tests condition first.
  - Continues looping until condition is false.
  - Example: Asking for people's names until 'zzz' is entered.
- Importance of not having excessive repeating lines in the code.

Stacking Structures
- Attaching structures end to end (e.g., sequence -> selection -> loop).
- Structures must be stacked without interweaving lines.
- Each structure must fully complete before stacking another.
Nesting Structures
- Placing one structure within another.
- Example: A sequence within a selection.
- Indentation is crucial for nested structures (e.g., use of curly braces in Java).
- Align nested structures vertically (e.g., EndIf aligns with If).
- No limits on the number of nesting levels.