# [Concepts] Paper 2
# CHAPTER 9: ALGORITHM DESIGN AND PROBLEM-SOLVING
## 9.1 COMPUTATIONAL THINKING SKILLS
### 9.1.1 Abstraction
**Definition:** The process of removing unnecessary details to focus on essential features.
**Need:**
- Manage complexity
- Create models of real-world systems
**Benefits:**
- Focus on what matters
- Reusable solutions
### 9.1.2 Decomposition
**Definition:** Breaking down complex problems into smaller, manageable sub-problems.
**Benefits:**
- Easier to solve smaller problems
- Can work on different parts independently
- Leads to modular programming (procedures/functions)
## 9.2 ALGORITHMS
### 9.2.1 Algorithm Representation
**Methods:**
- Structured English
- Flowchart
- Pseudocode
**Components:**
- Input
- Process
- Output
**Basic Constructs:**
- Sequence (order of execution)
- Selection (IF, CASE)
- Iteration (loops)
### 9.2.2 Pseudocode Guidelines
**Input/Output:**
<TEXT>
INPUT variable
OUTPUT variable/value
**Assignment:**
<TEXT>
variable ← value
**Selection:**
<TEXT>
IF condition THEN
statements
ELSE
statements
END IF
CASE OF variable
value1 : statement
value2 : statement
OTHERWISE : statement
END CASE
**Iteration:**
<TEXT>
FOR counter ← start TO end
statements
NEXT counter
WHILE condition
statements
END WHILE
REPEAT
statements
UNTIL condition
### 9.2.3 Stepwise Refinement
**Process:**
- Start with general solution
- Gradually add detail
- Continue until can be programmed
# CHAPTER 10: DATA TYPES AND STRUCTURES
## 10.1 DATA TYPES
### 10.1.1 Primitive Data Types
Type
Description
**INTEGER**
Whole numbers
**REAL**
Decimal numbers
**CHAR**
Single character
**STRING**
Sequence of characters
**BOOLEAN**
True/False
**DATE**
Date values
### 10.1.2 Records
**Definition:** A structure that holds a set of data of different types under one identifier.
**Purpose:**
- Group related data of different types
- Like a record in a database
**Example:**
<TEXT>
RECORD Employee
DECLARE EmpID : INTEGER
DECLARE Name : STRING
DECLARE Salary : REAL
END RECORD
## 10.2 ARRAYS
### 10.2.1 One-Dimensional Arrays
**Definition:** A collection of elements of the same type accessed by index.
**Terms:**
- Index: Position of element
- Lower bound: First index (usually 0 or 1)
- Upper bound: Last index
**Declaration:**
<TEXT>
DECLARE arrayname\[upperbound\] : TYPE
**Access:**
<TEXT>
arrayname\[index\]
### 10.2.2 Two-Dimensional Arrays
**Definition:** Array of arrays; elements accessed by row and column.
**Declaration:**
<TEXT>
DECLARE arrayname\[row, column\] : TYPE
### 10.2.3 Array Operations
**Linear Search:**
- Check each element sequentially
- Works on unsorted data
- O(n) time complexity
**Bubble Sort:**
- Compare adjacent elements
- Swap if in wrong order
- Repeat until sorted
- O(n²) time complexity
## 10.3 FILES
### 10.3.1 File Need
- Store data permanently
- Large amounts of data
- Data persistence between program runs
### 10.3.2 File Operations
**Opening:**
<TEXT>
OPENFILE filename FOR READ/WRITE/APPEND
**Reading:**
<TEXT>
READFILE filename, variable
**Writing:**
<TEXT>
WRITEFILE filename, variable
**Closing:**
<TEXT>
CLOSEFILE filename
## 10.4 ABSTRACT DATA TYPES (ADT)
### 10.4.1 Stack
**Characteristics:**
- LIFO (Last In, First Out)
- Add to top (push)
- Remove from top (pop)
**Operations:**
- Push: Add item to top
- Pop: Remove item from top
- Peek: View top item without removing
### 10.4.2 Queue
**Characteristics:**
- FIFO (First In, First Out)
- Add to rear (enqueue)
- Remove from front (dequeue)
### 10.4.3 Linked List
**Characteristics:**
- Dynamic structure
- Nodes contain data and pointer to next node
- Can grow/shrink easily
**Operations:**
- Add node
- Delete node
- Search
# CHAPTER 11: PROGRAMMING FUNDAMENTALS
## 11.1 PROGRAMMING BASICS
### 11.1.1 Variables and Constants
**Variable Declaration:**
**Choice of Loop:**
- FOR: When number of iterations known
- WHILE: When condition checked before first iteration
- REPEAT: When condition checked after at least one iteration
## 11.3 STRUCTURED PROGRAMMING
### 11.3.1 Procedures
**Definition:** A reusable block of code that performs a specific task.
**Declaration:**
<TEXT>
PROCEDURE name(parameter1, parameter2)
statements
END PROCEDURE
**Call:**
<TEXT>
CALL name(argument1, argument2)
**Parameters:**
- Passed by value: Copy of data passed
- Passed by reference: Actual data passed (can be modified)
### 11.3.2 Functions
**Definition:** Returns a value; used in expressions.
**Declaration:**
<TEXT>
FUNCTION name(parameter) RETURN type
statements
RETURN value
END FUNCTION
**Use:**
<TEXT>
result ← name(arguments)
# CHAPTER 12: SOFTWARE DEVELOPMENT
## 12.1 PROGRAM DEVELOPMENT LIFECYCLE
### 12.1.1 Stages
1. **Analysis:** Understand problem, identify requirements
2. **Design:** Create solution structure, algorithms
3. **Coding:** Write actual program code
4. **Testing:** Find and fix errors
5. **Maintenance:** Update and improve after delivery
### 12.1.2 Development Models
**Waterfall:**
- Sequential phases
- Each phase completes before next begins
- Good for well-defined requirements
**Iterative:**
- Develop in cycles
- Each iteration produces working version
- Allows feedback and improvement
**RAD (Rapid Application Development):**
- Quick development using pre-built components
- Emphasis on prototyping
- Fast user feedback
## 12.2 PROGRAM DESIGN
### 12.2.1 Structure Chart
**Purpose:** Decompose problem into sub-tasks
**Shows:**
- Modules/procedures/functions
- Parameters passed between modules
### 12.2.2 State-Transition Diagrams
**Purpose:** Document algorithm behavior
**Shows:**
- Different states
- Transitions between states
## 12.3 PROGRAM TESTING AND MAINTENANCE
### 12.3.1 Error Types