Decisions in Computational Thinking

Overview

In computational thinking, decisions are critical points where a program must choose between different actions based on specific conditions. These decisions influence the flow of control, determining which path the program follows. Understanding where and how decisions are made is essential for designing effective algorithms and programs.

What are Decisions in a Program?

• Definition: A decision is a point in a program where the next action depends on whether a certain condition is true or false.
• Purpose: To control the program's flow by choosing between different branches or paths.

Decision Structures:

IF Statements:

Used to execute a block of code if a condition is true.

IF temperature > 30 THEN
    PRINT "It's hot"
ELSE
    PRINT "It's not hot"
ENDIF

IF-ELSE-IF Ladder:

Handles multiple conditions.

IF score >= 90 THEN
    PRINT "Grade A"
ELSEIF score >= 80 THEN
    PRINT "Grade B"
ELSE
    PRINT "Grade C"
ENDIF

CASE/SWITCH Statements:

Used when multiple conditions are checked against a single variable.

CASE day OF
    "Monday": PRINT "Start of work week"
    "Friday": PRINT "End of work week"
    "Saturday", "Sunday": PRINT "Weekend"
ENDCASE

LOOPS with Conditions:

Decisions are also made within loops using WHILE, FOR, or REPEAT constructs.

WHILE attempts < 3 AND password != correct_password
    INPUT password
    attempts = attempts + 1
ENDWHILE

Identifying Decision Points in a Solution

1. Understand the Problem Requirements: Identify the conditions or criteria that affect the program's behaviour.
2. Locate Decision Points:

• Points where the program must choose between different actions based on conditions.
• Common scenarios:
• Validating user input.
• Determining program outputs based on input data.
• Handling different cases in a process.

3. Analyse Flow Control: Decisions create branches or loops, altering the program's execution path.

Example Scenarios

IF balance >= withdrawal_amount THEN
    DISPENSE cash
    UPDATE balance
ELSE
    PRINT "Insufficient funds"
ENDIF

IF score >= 80 THEN
    PRINT "Excellent"
ELSEIF score >= 50 THEN
    PRINT "Good"
ELSE
    PRINT "Needs Improvement"
ENDIF

How Decisions Affect Program Flow

1. Branching:

• Decisions create multiple branches in the program, leading to different outcomes based on conditions.

2. Looping:

• Decisions within loops determine how many times the loop will execute.

3. Early Exits:

• Decisions can lead to the early termination of a program or function.

4. Multiple Outcomes:

• Different decision paths can lead to varying outputs or behaviours depending on the inputs.

Tools for Representing Decisions

Flowcharts:

• Visual representation of decision points and their corresponding paths.
• Decision Symbol (Diamond): Represents a decision point.

Pseudocode:

• Describes decision-making processes in a structured, easy-to-read format.
• Useful for planning before coding.

Code Implementation:

• Translate decisions into actual program code using decision structures like IF, CASE, or loops.

Note Summary