Grade 11 - Fundamentals of Programming Notes

Computer Program

• A set of instructions that tells a computer what tasks to perform.
• The computer follows these instructions step by step.

Purpose of Programs

• All computer actions are based on the instructions given in programs.
• No task is done without being explicitly programmed.

Topics Covered in This Unit

• Programming languages: Tools used to write programs (e.g., Python, Java).
• Syntax: The rules of writing code correctly.
• Semantics: The meaning or logic behind the code instructions.

Language Used in This Unit

• The unit uses Python, a high-level programming language.
• Python is used to teach the basic concepts of programming in a simple and readable way

Types of Programming Languages

Machine Language

• A low-level language.
• Written in binary (1s and 0s).
• Understood directly by computers (no translation needed).
• Very fast and memory-efficient, but extremely hard for humans to write and understand.

Assembly Language

• Also a low-level language.
• Uses mnemonics (symbols) instead of 1s and 0s (e.g., MOV, ADD).
• Easier than machine language, but still difficult to use.
• Needs an Assembler to convert it into machine language.

High-Level Language

• Closer to human language (e.g., English-like words).
• Easy to learn and use.
• Examples: Python, Java, C, C++, C#, Perl, Ruby
• Requires translation into machine language using:
  • Compiler: Translates the whole program at once.
  • Interpreter: Translates and runs the program line by line.
  • Compiled Languages: C, C++, Java, C#
  • Interpreted Languages: Python, Perl, Ruby

Syntax and Semantics

Syntax

• The rules and structure of a programming language.
• Similar to grammar in human languages.
• If you break syntax rules, the program won’t run and will give a syntax error.

Semantics

• The meaning of the program statements (what the code actually does).
• A program with correct syntax can still behave wrongly due to logic errors.
• Logic error = The program runs but gives wrong results due to incorrect instructions.

Key Terms Recap

• Machine Language: Binary code directly executed by the CPU
• Assembly Language: Symbolic code (mnemonics) translated by an assembler
• High-Level Language: Human-friendly code translated by a compiler or interpreter
• Syntax: Rules for writing correct code
• Semantics: Meaning and behavior of the code
• Syntax Error: Mistake in grammar (code won't run)
• Logic Error: Mistake in meaning (code runs but behaves incorrectly)

Basics of Python

Python Programming Language

• Python is a high-level, easy-to-learn programming language.
• It is widely used for teaching beginners due to its simple syntax.
• Python is free and open-source.

Python's Integrated Development Environment (IDLE)

• IDLE stands for Integrated Development and Learning Environment.
• It is the default environment provided with Python for writing and executing Python code.
• IDLE includes:
  • Interactive Interpreter (Shell)
  • Text Editor

Interactive Interpreter (Python Shell)

• It is a textual user interface that allows users to:
  • Type and execute one line of code at a time.
  • Get immediate feedback or results.
• Opened automatically when you start IDLE.
• Best used for:
  • Simple testing
  • Trying out quick commands
  • Learning syntax step-by-step
• Limitation: Not suitable for writing and running multiple lines of code (programs).

Text Editor in IDLE

• Used to write multiple lines of Python code (programs).
• The written code can be saved as a .py file and executed with a single command.
• More convenient for:
  • Writing complete programs
  • Debugging
  • Saving and editing scripts

Using the Interactive Interpreter

• The Interactive Interpreter appears when you open IDLE.
• It includes the Python Shell, a text-based interface to type and run Python code line by line.
• When you type a command or expression and press Enter, Python immediately executes it and shows the result.
• Example: python print("Hello, world!")
  • Output:
    Hello, world!
• The print() function is used to display text or results on the screen.

Using the Text Editor

• The Text Editor in IDLE is used to write and save multiple lines of Python code (called a script).
• A Python script is saved with the .py extension.
• Steps to create a script:
  1. Open IDLE.
  2. Click File → New File to open the Text Editor.
  3. Type your code in the new window.
  4. Save the file with a .py extension (e.g., circle_area.py).
• To run the script:
  1. Go to Run → Run Module.
  2. The output appears in the Interactive Interpreter window (Python Shell).
• Example: Calculate the Area of a Circle
  • A sample script to calculate the area of a circle with radius 3:
    python radius = 3 area = 3.14 * radius * radius print("Area of the circle is:", area)
• After running, the output will be shown in the shell.

Variables and Data Types

Variables

• Definition: A variable is a memory location used to store data. In Python, variables are created when a value is assigned to them.
• Assignment Operator (=): Used to assign values.
  • Left side → variable
  • Right side → value or expression
• Examples:
  python x = 5 # Assigns 5 to variable x y = 5 + 9 # Assigns 14 to variable y
• Viewing Variable Values: Type the variable name and press Enter:
  python y # Output: 25 (if y = 25)
• Reassigning Values: Variables can be updated:
  python y = 30 # y now holds the value 30

Identifiers

• Definition: An identifier is the name given to a variable.
• Rules for Valid Identifiers:
  1. Must start with a letter or underscore (_)
  2. Remaining characters can be letters, numbers, or underscores
  3. Cannot be a Python keyword (e.g., if, while, def, etc.)
  4. Case-sensitive (x and X are different)
• Best Practice: Use self-descriptive identifiers (e.g., student_age instead of x) to improve code clarity.

Data Types

• Definition: A data type specifies the kind of value a variable can hold and the operations that can be performed on it.
• Common Built-in Data Types in Python:
  1. int → whole numbers (e.g., x = 10)
  2. float → decimal numbers (e.g., pi = 3.14)
  3. str → strings or text (e.g., name = "Alice")
  4. bool → Boolean values (True or False)
• Example of Data Types in Action:
  python a = 42 # a is an integer (int) b = 3.14 # b is a float c = "Hello" # c is a string (str) d = True # d is a Boolean (bool)
• Automatic Data Type Assignment: The data type is automatically determined by the value assigned to the variable.

Additional Concepts: Strings and the type() Function

• Strings Must Be in Quotation Marks:
  • In Python, string values must be enclosed in either single (') or double (") quotation marks.
  • Example:
    python name = "Alice" # Valid string greeting = 'Hello' # Also valid
• Determining Data Type with type() Function:
  • Python provides a built-in function called type() to check the data type of a variable.
  • Syntax:
    python type(variable_name)
  • Example:
    python x = 10 y = "Hello" print(type(x)) # Output: <class 'int'> print(type(y)) # Output: <class 'str'>

Data Type Conversion

Data type conversion refers to changing the value of one data type into another. Python supports two types of type conversion:

Implicit Type Conversion

• Definition: Done automatically by Python, without programmer intervention.
• Purpose: To prevent loss of data when performing operations involving different data types.
• How it works: Python converts smaller data types to larger ones, such as from int to float.
• Example: python x = 5 # int y = 3.2 # float z = x + y # z becomes float (8.2) print(type(z)) # Output: <class 'float'>
  • Here, x is an integer, and y is a float.
  • Python automatically converts x to float before performing the addition.
  • The result z becomes a float to maintain precision.

Explicit Type Conversion (Type Casting)

• Definition: Done manually by the programmer using built-in functions.
• Functions Used:
  • int() – converts to integer
  • float() – converts to floating-point number
  • str() – converts to string
• Syntax:
  python variable_name = data_type(value)
• Invalid Operation Example:
  python x = 5 # int y = "10" # str z = x + y # ERROR: can't add int and str
  Python raises a TypeError because it can't add a number (int) to text (str).
• Corrected with Explicit Conversion:
  python x = 5 y = "10" z = x + int(y) # y converted to int print(z) # Output: 15
  Here, int(y) converts the string "10" into the integer 10, allowing the addition to proceed correctly.

Summary Table

Statements and Expressions

What is a Statement?

• A statement is an instruction that Python can execute.
• It tells the computer to do something, like assigning a value, printing output, or making decisions.

Examples of Python Statements:

1. Assignment Statement
   • Assigns a value to a variable.
   • Example:
     python x = 10
2. Print Statement
   • Displays the value or result on the screen.
   • Example:
     python print("Hello, world!")
3. Control Statements These are used to control the flow of a program:
   • If Statement – used for decision making
     python if x > 5: print("x is greater than 5")
   • While Statement – repeats code while a condition is true
     python while x > 0: print(x) x = x - 1
   • For Statement – repeats code a specific number of times
     python for i in range(5): print(i)

What is an Expression?

• An expression is any combination of variables, values, and operators that evaluates to a value.
• Expressions are often part of statements.

Example of Expressions:

a = 5 + 3 # 5 + 3 is an expression, a = 8 is the statement

• 5 + 3 is the expression (evaluates to 8)
• a = 5 + 3 is the statement (assigns 8 to a)

Summary Table

Writing a Simple Program

Python Program

Write a program in the text editor that has the following elements:

• Accept the name, age, and Body Mass Index (BMI) of a person from the keyboard using the input() function,
• Convert the values to their appropriate data type,
• Display the values using the print() function

# Accepting input from the user
name = input("Enter your name: ")
age = int(input("Enter your age: "))  # Convert age to integer
bmi = float(input("Enter your BMI: "))  # Convert BMI to float

# Displaying the values
print("---- Personal Information ----")
print("Name:", name)
print("Age:", age)
print("BMI:", bmi)

Explanation:

• input() always returns a string, so:
  • int() is used to convert age to an integer.
  • float() is used to convert BMI to a decimal number.
• print() displays the collected and converted values in a readable format.

Understanding the input() Function in Python

• Prompt Message: When using input(), you can provide a prompt string that tells the user what to enter.

  Example:

  x = input("Enter an integer number: ")
  

• Return Type is Always a String: No matter what the user types (number, text, etc.), the value returned by input() is always of type string (str). So if you want another data type, like an integer or a float, you need to convert it explicitly.

• Type Conversion Example: To convert the string returned by input() into an integer, use int() like this:

  x = input("Enter an integer number: ")
  x = int(x) # Converts string to integer
  

• Assigning Input to Variables: The value returned by input() is typically stored in a variable, since input() acts like an expression that returns a value.

  Example:

  age = input("Enter your age: ")
  

Here’s a clear and simple example of a Python program that uses input() to accept the radius of a circle from the user, and print() to display the area and circumference:

# Accept radius from the user
radius = float(input("Enter the radius of the circle: "))

# Calculate area and circumference
area = 3.1416 * radius * radius
circumference = 2 * 3.1416 * radius

# Display the results
print("Area of the circle:", area)
print("Circumference of the circle:", circumference)

Explanation:

• input() reads data as a string from the keyboard.
• float() converts the input string into a floating-point number so we can do math.
• The program calculates:
  • Area = $π \times radius^2$
  • Circumference = $2 \times π \times radius$
• print() outputs the calculated values on the screen.