Lesson 2: Control Flow

Let’s dive into Lesson 2: Control Flow, which includes conditional statements, loops, and basic algorithms. This lesson will teach you how to control the flow of a program based on conditions and repetitions while introducing simple algorithmic logic.

1. Conditional Statements

Overview

Conditional statements allow a program to execute specific blocks of code based on certain conditions.

• if: Executes a block of code if a condition is true.
• if-else: Provides an alternative block of code if the condition is false.
• else if: Tests multiple conditions.
• switch: An alternative to multiple if-else statements, useful for checking specific values.

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Code Example: if-else and else if

public class ConditionalExample {
    public static void main(String[] args) {
        int age = 18;

        if (age >= 18) {
            System.out.println("You are an adult.");
        } else if (age >= 13) {
            System.out.println("You are a teenager.");
        } else {
            System.out.println("You are a child.");
        }
    }
}

Expected Output:

You are an adult.

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Code Example: switch

public class SwitchExample {
    public static void main(String[] args) {
        int day = 3; // Representing Wednesday

        switch (day) {
            case 1:
                System.out.println("Monday");
                break;
            case 2:
                System.out.println("Tuesday");
                break;
            case 3:
                System.out.println("Wednesday");
                break;
            default:
                System.out.println("Invalid day");
        }
    }
}

Expected Output:

Wednesday

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2. Loops

Overview

Loops allow a block of code to repeat multiple times.

• for: Repeats a block of code for a known number of iterations.
• while: Repeats a block of code while a condition is true.
• do-while: Executes a block of code at least once before checking the condition.

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Code Example: for Loop

public class ForLoopExample {
    public static void main(String[] args) {
        for (int i = 1; i <= 5; i++) {
            System.out.println("Iteration " + i);
        }
    }
}

Expected Output:

Iteration 1
Iteration 2
Iteration 3
Iteration 4
Iteration 5

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Code Example: while Loop

public class WhileLoopExample {
    public static void main(String[] args) {
        int i = 1;

        while (i <= 5) {
            System.out.println("Count: " + i);
            i++;
        }
    }
}

Expected Output:

Count: 1
Count: 2
Count: 3
Count: 4
Count: 5

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Code Example: do-while Loop

public class DoWhileExample {
    public static void main(String[] args) {
        int i = 1;

        do {
            System.out.println("Number: " + i);
            i++;
        } while (i <= 5);
    }
}

Expected Output:

Number: 1
Number: 2
Number: 3
Number: 4
Number: 5

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3. Basic Algorithms

Algorithm 1: Find the Largest of Three Numbers

public class LargestNumber {
    public static void main(String[] args) {
        int a = 10, b = 20, c = 15;

        if (a >= b && a >= c) {
            System.out.println("The largest number is: " + a);
        } else if (b >= a && b >= c) {
            System.out.println("The largest number is: " + b);
        } else {
            System.out.println("The largest number is: " + c);
        }
    }
}

Expected Output:

The largest number is: 20

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Algorithm 2: Sum of Numbers from 1 to N

import java.util.Scanner;

public class SumToN {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        System.out.print("Enter a positive number: ");
        int n = scanner.nextInt();

        int sum = 0;

        for (int i = 1; i <= n; i++) {
            sum += i;
        }

        System.out.println("The sum of numbers from 1 to " + n + " is: " + sum);
    }
}

Sample Console Interaction:

Enter a positive number: 5
The sum of numbers from 1 to 5 is: 15

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Algorithm 3: Multiplication Table

import java.util.Scanner;

public class MultiplicationTable {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        System.out.print("Enter a number: ");
        int number = scanner.nextInt();

        for (int i = 1; i <= 10; i++) {
            System.out.println(number + " x " + i + " = " + (number * i));
        }
    }
}

Sample Console Interaction:

Enter a number: 3
3 x 1 = 3
3 x 2 = 6
...
3 x 10 = 30

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