Control Structures – Sequence, Selection, Repetition, if-else & Loops

This article is a concept explanation about control structures – including exam questions and tags.

In a Nutshell

Control structures determine the flow of an algorithm through decisions, repetitions, and sequences. They are essential for controlling program logic.

Compact Technical Description

Control structures are fundamental building blocks in algorithms that control the flow of program execution. There are three main types: Sequence (instructions executed one after another), Selection (e.g., if/else – decisions), and Repetition (e.g., loops like for or while). Through them, an algorithm can flexibly respond to different inputs or situations. Conditional statements allow different paths to be taken based on truth values. Loops enable instructions to be executed multiple times as long as a specific condition is met.

Exam-Relevant Key Points

• Three main types: Sequence, Selection, Repetition
• Conditional branches: if, else if, else
• Loop types: for, while, do-while
• Control structures influence flow logic
• Loops should terminate (exit condition)

Core Components

1. Sequence (linear execution)
2. Selection (e.g., if/else, switch)
3. Repetition (e.g., while, for)
4. Conditions (Boolean expressions)
5. Loop control (break, continue)

Practical Example

// Example: Check if a number is even
if (number % 2 == 0) then
    output("Number is even")
else
    output("Number is odd")

Explanation: The modulo operator checks if a number is divisible by 2 without remainder. Depending on the result, an appropriate message is output.

Advantages and Disadvantages

Advantages

• Increases code readability and structure
• Allows dynamic flows based on conditions
• Supports reusability through loops

Disadvantages

• Complex nested structures can be unclear
• Infinite loops possible with incorrect conditions
• Error-prone with incorrectly defined conditions

Typical Exam Questions (with Brief Answers)

1. Three types of control structures? Sequence, Selection, Repetition.
2. if-branch used? For conditional execution of statements based on a truth value.
3. Difference while vs. for-loop? For-loops contain initialization, condition, and increment; while-loops only the condition.
4. “break” in a loop? Terminates the loop prematurely.
5. do-while loop use? When the loop should run at least once.
6. Avoid infinite loop? Through a meaningful exit condition within the loop.
7. Role of conditions in control structures? Control whether and how often a specific code section is executed.

Most Important Sources

1. https://en.wikipedia.org/wiki/Control_flow
2. https://www.w3schools.com/cs/cs_conditions.php
3. https://www.geeksforgeeks.org/control-structures-in-c/