Introduction to Control Flow: Dictating Program Logic

Control Flow defines the specific order in which instructions are executed in a program. Programs initially run sequentially (top-to-bottom), but true software needs the ability to divert, repeat, or skip steps. Control flow constructs provide the critical mechanism to dictate this complex logic path, moving execution beyond simple fixed sequencing.

1. Selection Structures (Conditional Logic)

Selection allows a program to make dynamic decisions. It executes a specific block of code only if a stated condition evaluates to True. If the condition is False, a different block of code (or none at all) is executed.

Conceptual Example: IF (The user clicks the button) THEN (Load the next screen) ELSE (Stay on current screen).

2. Core Components of Decision Making

Boolean Expression (The Condition): A statement that must evaluate strictly to either $T$ (True) or $F$ (False). This result dictates the program's path forward.
Relational Operators: Tools like "greater than" (>), "less than" (<), or "equal to" (==) used to compare values and construct the core condition.
Logical Operators (AND, OR, NOT): Mechanisms used to combine multiple simple Boolean expressions into a single, more complex decision criterion.

Critical Requirement

Mastery of control flow is essential because it allows programs to become dynamic and responsive, reacting to real-time inputs, user interaction, or changing data states, instead of running a static, predefined script.

TERMINAL bash — 80x24

> Ready. Click "Run" to execute.

Question 1

What dictates the program path when simple sequential execution is insufficient?

Variable declaration

Control Flow Structures

Comments

Data types

Question 2

What are the two possible outcomes of a Boolean Expression used in selection logic?

Integer or Float

True or False

String or List

Null or Empty

Question 3

What does an 'if' statement fundamentally allow a program to do?

Repeat a block of code

Choose between two or more execution paths

Store data temporarily

Print text to the console

Challenge: Decision Making Overview

Outline the logic path.

A banking application must decide whether to grant a user access based on two conditions: 1) The account status must be 'Active', AND 2) The password provided must match the stored password.

Step 1

What type of logic links these two conditions to ensure access is granted?

Solution:
Use the AND logical operator. Access requires that condition 1 is True and condition 2 is True. If either is False, access is denied.

Step 2

If the account status fails (e.g., it is 'Locked'), which path is taken?

Solution:
The 'False' path is taken. Since both conditions are required (AND logic), the program does not need to check the password if the account status already failed.

Step 3

If the conditions are met, what happens to the control flow?

Solution:
The control flow branches into the 'True' code block, executing the instructions within (e.g., logging the user in), then resumes the normal sequential flow after the conditional block ends.