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Module 2: Basic Pascal Programming – Master Variables, Operators, and Control Structures

Module 2: Basic Pascal Programming

Lesson 3: Variables, Data Types, and Operators

Objective: Teach learners how to declare variables, use different data types, and perform operations in Pascal.

Understanding Variables and Data Types:

Variables: Named storage locations that hold data. Variables must be declared before use.

var
  age: Integer;
  name: String;
  isStudent: Boolean;

In this example:

  • age: is an integer variable that can hold whole numbers.
  • name: is a string variable that can hold text.
  • isStudent: is a Boolean variable that can hold a True or False value.
Diagram showing different types of variables in Pascal with examples like Integer, String, Boolean.

A diagram showing different types of variables in Pascal, including Integer, String, and Boolean, with relevant examples.

Using Operators in Pascal:

In Pascal, operators are used to perform various operations on variables and values. These operators can be categorized into three main types: arithmetic, relational, and logical operators.

Arithmetic Operators:

Arithmetic operators are used to perform mathematical operations on numerical values. Here are some simple examples:

  • Addition (+): Adds two values together.
  • var sum: Integer;
    begin
      sum := 10 + 5;  // sum now equals 15
    end;

    In this example, the + operator adds the values 10 and 5, and stores the result in the variable sum.

  • Subtraction (-): Subtracts one value from another.
  • var difference: Integer;
    begin
      difference := 10 - 5;  // difference now equals 5
    end;

    Here, the - operator subtracts 5 from 10, and the result is stored in the variable difference.

  • Multiplication (*): Multiplies two values.
  • var product: Integer;
    begin
      product := 10 * 5;  // product now equals 50
    end;

    The * operator multiplies 10 and 5, with the result stored in product.

  • Division (/): Divides one value by another.
  • var quotient: Real;
    begin
      quotient := 10 / 5;  // quotient now equals 2.0
    end;

    The / operator divides 10 by 5, and since the result is a real number (2.0), it is stored in a Real type variable called quotient.

  • Modulus (mod): Returns the remainder of a division operation.
  • var remainder: Integer;
    begin
      remainder := 10 mod 3;  // remainder now equals 1
    end;

    The mod operator divides 10 by 3, and returns the remainder (1) rather than the quotient. The result is stored in remainder.

Relational Operators:

Relational operators are used to compare two values. They return a Boolean result (True or False). Here’s how they work:

  • Equal to (=): Checks if two values are equal.
  • var isEqual: Boolean;
    begin
      isEqual := (5 = 5);  // isEqual is True
    end;

    In this case, the = operator checks if 5 is equal to 5. Since it is, the Boolean variable isEqual is set to True.

  • Greater than (>): Checks if the first value is greater than the second.
  • var isGreater: Boolean;
    begin
      isGreater := (10 > 5);  // isGreater is True
    end;

    The > operator checks if 10 is greater than 5, which is True, so isGreater is set to True.

  • Less than (<): Checks if the first value is less than the second.
  • var isLess: Boolean;
    begin
      isLess := (3 < 5);  // isLess is True
    end;

    The < operator checks if 3 is less than 5, which is True, so isLess is set to True.

Logical Operators:

Logical operators are used to perform logical operations, typically on Boolean values. Here are some examples:

  • AND: Returns True if both conditions are True.
  • var result: Boolean;
    begin
      result := (5 > 0) AND (3 > 0);  // result is True
    end;

    The AND operator checks if both conditions (5 > 0 and 3 > 0) are True. Since they are, result is set to True.

  • OR: Returns True if at least one condition is True.
  • var result: Boolean;
    begin
      result := (5 > 0) OR (3 < 0);  // result is True
    end;

    The OR operator checks if either condition is True. Since 5 > 0 is True, result is set to True, regardless of the second condition.

  • NOT: Reverses the Boolean value.
  • var result: Boolean;
    begin
      result := NOT (5 > 10);  // result is True
    end;

    The NOT operator reverses the Boolean value of the expression. Since 5 > 10 is False, result is set to True.

Reading and Writing Data:

In Pascal, you can use the writeln and readln functions to interact with the user.

  • writeln: Outputs text to the screen.
  • writeln('Hello, World!');

    This command prints "Hello, World!" to the console.

  • readln: Reads input from the user.
  • var name: String;
    begin
      writeln('Enter your name:');
      readln(name);
      writeln('Hello, ', name, '!');
    end;

    In this example, readln pauses the program to allow the user to input their name, which is then stored in the name variable and displayed back to the user.

Exercises:

  • Using the arithmetic operators you've learned, write a program that calculates the area of a rectangle given its width and height.
  • Create a program that determines if a number is even or odd using the modulus operator and an If-Else statement.

Lesson 4: Control Structures

Objective: Introduce learners to conditional statements and loops, essential for controlling the flow of a program.

Understanding Control Structures:

Control structures are fundamental in programming as they allow the flow of a program to be altered based on conditions or repeated actions. In Pascal, the most common control structures are If-Else statements and loops (For, While, and Repeat-Until).

If-Else Statement:

The If-Else statement is used to execute a block of code if a specified condition is true, and another block of code if the condition is false. This allows the program to make decisions based on certain conditions.

if condition then
  statement1
else
  statement2;

For example:

var age: Integer;
begin
  age := 20;
  if age >= 18 then
    writeln('You are an adult.')
  else
    writeln('You are a minor.');
end;

This example shows how the If-Else statement can be used to check if a person is an adult based on their age.

Loops in Pascal:

Loops allow you to execute a block of code multiple times. Pascal provides three types of loops: For, While, and Repeat-Until.

For Loop:

The For loop is used when the number of iterations is known. It repeats a block of code a specific number of times.

var i: Integer;
begin
  for i := 1 to 10 do
    writeln(i);
end;

This loop prints numbers from 1 to 10.

While Loop:

The While loop continues to execute as long as the specified condition remains true.

var num: Integer;
begin
  num := 10;
  while num > 0 do
  begin
    writeln('Countdown: ', num);
    num := num - 1;
  end;
end;

In this example, the loop counts down from 10 until num is no longer greater than 0.

Repeat-Until Loop:

The Repeat-Until loop is similar to the While loop, but the condition is checked after the loop's body has executed, ensuring that the loop runs at least once.

var num: Integer;
begin
  repeat
    writeln('Enter a number: ');
    readln(num);
  until num > 0;
end;

This loop continues asking for input until the user enters a positive number.

Exercises:

  • Write a program that asks the user for a number and then prints whether it's positive, negative, or zero.
  • Create a loop that prints all the numbers from 1 to 100.

Lesson 5: Procedures and Functions

Objective: Teach learners how to create and use procedures and functions to organize code and perform specific tasks.

Understanding Procedures and Functions:

In Pascal, procedures and functions are used to break down a program into smaller, manageable pieces. This makes the code more modular and easier to understand, debug, and maintain.

Procedures:

A procedure is a block of code that performs a specific task but does not return a value. It is called by its name, and the program control passes to the procedure when called.

procedure Greet;
begin
  writeln('Hello, World!');
end;

To call this procedure, simply write:

begin
  Greet;
end;

This will print "Hello, World!" when the procedure Greet is called.

Functions:

A function is similar to a procedure, but it returns a value. Functions are used when a task needs to produce a result that can be used elsewhere in the program.

function AddNumbers(a, b: Integer): Integer;
begin
  AddNumbers := a + b;
end;

To call this function and use its result, write:

var sum: Integer;
begin
  sum := AddNumbers(5, 10);
  writeln('Sum: ', sum);
end;

This will calculate the sum of 5 and 10 and print "Sum: 15".

Scope and Lifetime of Variables:

When using procedures and functions, it's important to understand the concept of variable scope. Variables declared within a procedure or function are local to that block and cannot be accessed outside of it.

var
  globalVar: Integer;

procedure Example;
var
  localVar: Integer;
begin
  localVar := 10;
  writeln('Local Variable: ', localVar);
end;

begin
  globalVar := 5;
  Example;
  writeln('Global Variable: ', globalVar);
end;

In this example, localVar is local to the procedure Example, while globalVar is accessible both inside and outside of the procedure.

Exercises:

  • Write a procedure that takes a person's name as an argument and prints a personalized greeting.
  • Create a function that calculates and returns the factorial of a given number.

Answers to Exercises

Lesson 3:

Exercise 1: Write a program that calculates the area of a rectangle given its width and height.

var
  width, height, area: Integer;
begin
  width := 10;
  height := 5;
  area := width * height;
  writeln('The area of the rectangle is: ', area);
end.

Exercise 2: Create a program that determines if a number is even or odd using the modulus operator.

var
  num: Integer;
begin
  writeln('Enter a number: ');
  readln(num);
  if num mod 2 = 0 then
    writeln(num, ' is even')
  else
    writeln(num, ' is odd');
end;

In this example, the program checks if the remainder when dividing the number by 2 is zero. If it is, the number is even; otherwise, it’s odd.

Lesson 4:

Exercise 1: Write a program that asks the user for a number and then prints whether it's positive, negative, or zero.

var
  num: Integer;
begin
  writeln('Enter a number: ');
  readln(num);
  if num > 0 then
    writeln('The number is positive')
  else if num < 0 then
    writeln('The number is negative')
  else
    writeln('The number is zero');
end;

Exercise 2: Create a loop that prints all the numbers from 1 to 100.

var
  i: Integer;
begin
  for i := 1 to 100 do
    writeln(i);
end;

Lesson 5:

Exercise 1: Write a procedure that takes a person's name as an argument and prints a personalized greeting.

procedure GreetPerson(name: String);
begin
  writeln('Hello, ', name, '!');
end;

begin
  GreetPerson('Alice');
end;

Exercise 2: Create a function that calculates and returns the factorial of a given number.

function Factorial(n: Integer): Integer;
var
  i, result: Integer;
begin
  result := 1;
  for i := 1 to n do
    result := result * i;
  Factorial := result;
end;

begin
  writeln('Factorial of 5 is: ', Factorial(5));
end;

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