Types of Loops:

• for loop - Known number of iterations
• while loop - Entry-controlled loop
• do-while loop - Exit-controlled loop
• enhanced for loop - For arrays/collections

Key Components:

• Initialization: Starting point
• Condition: Loop continuation test
• Update: Loop variable modification
• Body: Statements to execute

Syntax & Structure:

for (initialization; condition; update) {
    // loop body
}

// Components breakdown:
// 1. initialization - executed once
// 2. condition - checked before each iteration
// 3. update - executed after each iteration

Basic Examples:

// Print numbers 1 to 10
for (int i = 1; i <= 10; i++) {
    System.out.println(i);
}

// Count down from 10 to 1
for (int i = 10; i >= 1; i--) {
    System.out.println("Countdown: " + i);
}

// Even numbers from 2 to 20
for (int i = 2; i <= 20; i += 2) {
    System.out.println("Even: " + i);
}

Practical Applications:

// Sum of first n natural numbers
int n = 10;
int sum = 0;
for (int i = 1; i <= n; i++) {
    sum += i;
}
System.out.println("Sum: " + sum); // 55

// Factorial calculation
int number = 5;
long factorial = 1;
for (int i = 1; i <= number; i++) {
    factorial *= i;
}
System.out.println(number + "! = " + factorial); // 120

Syntax & Characteristics:

while (condition) {
    // loop body
    // update statement (if needed)
}

// Entry-controlled loop:
// - Condition checked before execution
// - May not execute at all if condition is false
// - Used when number of iterations is unknown

Basic Examples:

// Print numbers 1 to 5
int i = 1;
while (i <= 5) {
    System.out.println(i);
    i++; // Don't forget to update!
}

// Input validation loop
Scanner scanner = new Scanner(System.in);
int number;
while (true) {
    System.out.print("Enter a positive number: ");
    number = scanner.nextInt();
    if (number > 0) {
        break; // Exit loop when valid input
    }
    System.out.println("Please enter a positive number!");
}

Real-world Applications:

// Password verification system
String correctPassword = "secret123";
String userInput = "";
Scanner scanner = new Scanner(System.in);
int attempts = 0;
int maxAttempts = 3;

while (!userInput.equals(correctPassword) && attempts < maxAttempts) {
    System.out.print("Enter password: ");
    userInput = scanner.nextLine();
    attempts++;
    
    if (!userInput.equals(correctPassword)) {
        int remaining = maxAttempts - attempts;
        if (remaining > 0) {
            System.out.println("Incorrect! " + remaining + " attempts left.");
        }
    }
}

if (userInput.equals(correctPassword)) {
    System.out.println("Access granted!");
} else {
    System.out.println("Access denied! Too many failed attempts.");
}

Syntax & Key Features:

do {
    // loop body
    // update statement (if needed)
} while (condition);

// Exit-controlled loop:
// - Body executed at least once
// - Condition checked after execution
// - Notice the semicolon after while!

Basic Examples:

// Menu system - executes at least once
int choice;
Scanner scanner = new Scanner(System.in);

do {
    System.out.println("\n=== MENU ===");
    System.out.println("1. Option A");
    System.out.println("2. Option B");
    System.out.println("3. Exit");
    System.out.print("Enter choice: ");
    choice = scanner.nextInt();
    
    switch (choice) {
        case 1: System.out.println("You chose A"); break;
        case 2: System.out.println("You chose B"); break;
        case 3: System.out.println("Goodbye!"); break;
        default: System.out.println("Invalid choice!");
    }
} while (choice != 3);

Practical Applications:

// Number guessing game
Random random = new Random();
int secretNumber = random.nextInt(100) + 1; // 1-100
int guess;
int attempts = 0;
Scanner scanner = new Scanner(System.in);

System.out.println("Guess the number between 1-100!");

do {
    System.out.print("Enter your guess: ");
    guess = scanner.nextInt();
    attempts++;
    
    if (guess < secretNumber) {
        System.out.println("Too low! Try higher.");
    } else if (guess > secretNumber) {
        System.out.println("Too high! Try lower.");
    } else {
        System.out.println("Congratulations! You got it!");
        System.out.println("It took you " + attempts + " attempts.");
    }
} while (guess != secretNumber);

// Dice rolling until double 6
Random dice = new Random();
int dice1, dice2;
int rolls = 0;

do {
    dice1 = dice.nextInt(6) + 1;
    dice2 = dice.nextInt(6) + 1;
    rolls++;
    System.out.println("Roll " + rolls + ": " + dice1 + ", " + dice2);
} while (dice1 != 6 || dice2 != 6);

System.out.println("Double 6! It took " + rolls + " rolls.");

Syntax for Arrays:

// Traditional for loop
int[] numbers = {10, 20, 30, 40, 50};
for (int i = 0; i < numbers.length; i++) {
    System.out.println(numbers[i]);
}

// Enhanced for loop (for-each)
for (int num : numbers) {
    System.out.println(num);
}

Array Processing Examples:

// Sum of array elements
int[] marks = {85, 90, 78, 92, 88};
int total = 0;

for (int mark : marks) {
    total += mark;
}
double average = total / (double) marks.length;
System.out.println("Average: " + average);

// Find maximum in array
int[] values = {15, 23, 8, 45, 12, 67, 34};
int max = values[0];

for (int value : values) {
    if (value > max) {
        max = value;
    }
}
System.out.println("Maximum: " + max);

String Array Processing:

// Process array of strings
String[] subjects = {"Math", "Physics", "Chemistry", "Biology"};

System.out.println("Subjects offered:");
for (String subject : subjects) {
    System.out.println("- " + subject);
}

// Count specific elements
String[] colors = {"red", "blue", "green", "red", "yellow", "red"};
int redCount = 0;

for (String color : colors) {
    if (color.equals("red")) {
        redCount++;
    }
}
System.out.println("Red appears " + redCount + " times");

2D Array Processing:

// Process 2D array
int[][] matrix = {
    {1, 2, 3},
    {4, 5, 6},
    {7, 8, 9}
};

System.out.println("Matrix elements:");
for (int[] row : matrix) {
    for (int element : row) {
        System.out.print(element + " ");
    }
    System.out.println();
}

Basic Nested Loop Structure:

// Outer loop controls rows
for (int i = 1; i <= 3; i++) {
    System.out.println("Outer loop: " + i);
    
    // Inner loop controls columns
    for (int j = 1; j <= 4; j++) {
        System.out.println("  Inner loop: " + j);
    }
}

Multiplication Table:

// Generate multiplication tables 1-5
for (int table = 1; table <= 5; table++) {
    System.out.println("\nTable of " + table + ":");
    
    for (int i = 1; i <= 10; i++) {
        int result = table * i;
        System.out.println(table + " x " + i + " = " + result);
    }
}

2D Array Operations:

// Initialize and display 2D array
int rows = 3, cols = 4;
int[][] matrix = new int[rows][cols];

// Fill matrix with values
for (int i = 0; i < rows; i++) {
    for (int j = 0; j < cols; j++) {
        matrix[i][j] = (i + 1) * (j + 1);
    }
}

// Display matrix
System.out.println("Matrix:");
for (int i = 0; i < rows; i++) {
    for (int j = 0; j < cols; j++) {
        System.out.print(matrix[i][j] + "\t");
    }
    System.out.println();
}

Finding Patterns:

// Find all prime number pairs (twin primes)
for (int i = 2; i <= 100; i++) {
    if (isPrime(i) && isPrime(i + 2)) {
        System.out.println("Twin primes: " + i + ", " + (i + 2));
    }
}

// Helper method to check if number is prime
public static boolean isPrime(int n) {
    if (n <= 1) return false;
    for (int i = 2; i <= Math.sqrt(n); i++) {
        if (n % i == 0) return false;
    }
    return true;
}

break Statement:

Terminates the loop immediately and transfers control to the statement after the loop.

// Find first number divisible by 7
for (int i = 1; i <= 100; i++) {
    if (i % 7 == 0) {
        System.out.println("First number divisible by 7: " + i);
        break; // Exit loop immediately
    }
}

// Search in array
int[] numbers = {5, 12, 8, 21, 3, 15, 7};
int target = 21;
boolean found = false;

for (int num : numbers) {
    if (num == target) {
        System.out.println("Found " + target + " in the array!");
        found = true;
        break; // Stop searching once found
    }
}

if (!found) {
    System.out.println(target + " not found in array.");
}

continue Statement:

Skips the rest of the current iteration and continues with the next iteration.

// Print only odd numbers from 1 to 10
for (int i = 1; i <= 10; i++) {
    if (i % 2 == 0) {
        continue; // Skip even numbers
    }
    System.out.println("Odd number: " + i);
}

// Process only positive numbers
int[] values = {5, -2, 8, -1, 12, -7, 3};

for (int value : values) {
    if (value < 0) {
        continue; // Skip negative numbers
    }
    
    // Process positive numbers
    System.out.println("Processing positive: " + value);
    int square = value * value;
    System.out.println("Square: " + square);
}