pseudocode using the three basic constructs of sequence, decision, and iteration

9.2 Algorithms

Pseudocode Basics

Pseudocode is a simple, human‑readable way to describe how an algorithm works. It uses three core constructs:

• Sequence – steps executed one after another.
• Decision – choose between two or more paths (if‑then‑else).
• Iteration – repeat a block of steps (for, while).

Sequence Example

1. Read input number n
2. Set sum = 0
3. sum = sum + n
4. Output sum

Decision Example

1. Read temperature T
2. IF T > 30 THEN
3.     Output "Hot day"
4. ELSE
5.     Output "Cool day"
6. ENDIF

Iteration Example

1. Read n
2. FOR i = 1 TO n DO
3.     Output i
4. END FOR

Combining Constructs

Algorithms often mix all three constructs. Below is a classic example: computing the factorial of a number.

Common Mistakes to Avoid

• Using real programming language syntax (e.g., semicolons, braces).
• Omitting the END IF or END FOR statements.
• Not clearly indicating the start and end of loops.
• Mixing up FOR and WHILE when the condition is not a simple counter.

Quick Practice Problem

Write pseudocode to find the largest number in a list of m integers.

1. Read m and the list of numbers.
2. Set max = first number.
3. FOR each remaining number x DO
4.  IF x > max THEN max = x
5. END FOR
6. Output max

Emoji Summary

• 🔢 Sequence – steps in order.
• ❓ Decision – choose a path.
• 🔄 Iteration – repeat steps.
• ?? Result – final output.