Algorithm Design Lecture Notes

Definition of Algorithm

• An algorithm is a step-by-step procedure for solving a problem.
• It consists of a sequence of procedures to complete a specific task.
• Can involve:
  • Sequential execution
  • Decision making
  • Repetition
• Does not follow grammatical rules; no strict syntax.
• Represents a high-level solution to a problem.

Types of Algorithm Representation

1. Pseudocode

   • English-like format for instructions.
   • Used to plan logical steps for programming problems.
   • Preferred by some programmers for its closeness to programming languages (C++, Python, etc.).

2. Flowcharting

   • Graphical representation using conventional symbols.
   • Shows the sequence of events pictorially.
   • Two types of flowcharts:
     • System Flowchart: Total picture without every detail.
     • Program Flowchart: Depicts main segments of a complete computer program (focus of this lecture).

Flowcharting Symbols

1. Terminal Symbol

   • Represents the start and end of the flowchart.
   • Label can include “Start” or “End.”

2. Initialization/Preparation Symbol

   • Used for defining constants or variables at the start.

3. Input and Output Symbol

   • Represents input values and outputs.

4. Decision Box

   • Handles conditions; shows branching in the flow.

5. Process Box

   • Used for arithmetic operations (e.g. summing numbers).

6. Flow Line

   • Connects symbols within the flowchart.

7. On-page Connector

   • Connects segments on the same page that lack space.

8. Off-page Connector

   • Connects flowcharts that spill over to another page; labeled with letters or numbers.

General Logic in Flowcharting and Pseudocode

1. Sequential Flow
2. Branching (Conditional/Selection)
3. Looping (Iterative Program Structure)
4. Combination (mix of sequential, branching, and looping)

Key Elements for Flowcharts and Pseudocode

• Input, Processing, and Output: Essential for programming structure.

Program Elements and Structure

1. Constant
   • A literal value that does not change during execution.
   • Types:
     • Numeric Constant: Integer or real numbers (e.g. 10, -28, 3.4).
     • Character Constant: Enclosed in single quotation marks (e.g. 'A', '%', '.').

Examples of Numeric Constants

• Valid: 10, -28, 3.4, -0.413, 0, 201.
• Invalid Examples:
  • 10,000 (omit comma)
  • 14.3$ (omit dollar sign)
  • 10 miles/hour (omit unit)
  • One half (use 0.5 instead).

Examples of Character Constants

• Valid: 'A', '%', '.', 'g'.
• Note: Numeric values enclosed in single quotes represent character constants, not numeric constants.

Conclusion

• Understanding algorithm design is crucial for programming, ensuring clarity through pseudocode and flowcharts.