IT 9626 - Algorithms and Flowcharts

Objective: Use Pseudo-code (INPUT, WRITE, FOR, WHILE)

This section provides detailed notes on algorithms and flowcharts, focusing on the use of pseudo-code with the keywords INPUT, WRITE, FOR, and WHILE. We will cover fundamental concepts, examples, and best practices for designing and documenting algorithms.

What is an Algorithm?

An algorithm is a finite sequence of well-defined, computer-implementable instructions that leads to the solution of a problem. It's a step-by-step procedure.

Flowcharts

Flowcharts are diagrams that visually represent the steps in an algorithm. They use standardized symbols to show the flow of control. Flowcharts are a valuable tool for planning and documenting algorithms before coding.

Common Flowchart Symbols

• Start/Stop: Oval
• Process: Rectangle
• Input/Output: Parallelogram
• Decision: Diamond
• Flow Lines: Arrows

Pseudo-code

Pseudo-code is an informal way of describing an algorithm. It uses a combination of natural language and programming-like constructs to outline the steps. It's easier to read and understand than actual code, but it's more structured than plain English.

Key Pseudo-code Keywords

• INPUT: Used to get data from the user or a file.
• WRITE: Used to display output to the user or a file.
• FOR: Used to repeat a block of code a specified number of times.
• WHILE: Used to repeat a block of code as long as a condition is true.

Example 1: Calculating the Area of a Rectangle

Let's design an algorithm to calculate the area of a rectangle. The algorithm will take the length and width as input and output the area.

Flowchart

Pseudo-code

Step	Description
1	START
2	INPUT length, width
3	Calculate area = length * width
4	WRITE area
5	STOP

Example 2: Finding the Largest of Three Numbers

Here's an algorithm to find the largest of three numbers using a `FOR` loop and a `WHILE` loop.

Flowchart

Pseudo-code

Step	Description
1	START
2	INPUT num1, num2, num3
3	SET largest = num1
4	FOR i = 2 TO 3
5	IF num(i) > largest THEN
6	SET largest = num(i)
7	ENDIF
8	ENDFOR
9	WRITE largest
10	STOP

Example 3: Checking if a Number is Even or Odd

This algorithm uses a `WHILE` loop to determine if a number is even or odd.

Flowchart

Pseudo-code

Step	Description
1	START
2	INPUT number
3	WHILE number mod 2 <> 0
4	WRITE "Odd"
5	number = number / 2
6	ENDWHILE
7	WRITE "Even"
8	STOP

Best Practices

• Use clear and concise language.
• Indicate the flow of control clearly.
• Consider edge cases and error handling.
• Test your algorithms with sample inputs.