Control Structures

int age = 18;

if (age >= 18)
{
    Console.WriteLine("You are an adult.");
}

// Single line if (without braces)
if (age >= 18) Console.WriteLine("Eligible to vote.");

int score = 85;

if (score >= 90)
{
    Console.WriteLine("Grade: A");
}
else if (score >= 80)
{
    Console.WriteLine("Grade: B");
}
else if (score >= 70)
{
    Console.WriteLine("Grade: C");
}
else if (score >= 60)
{
    Console.WriteLine("Grade: D");
}
else
{
    Console.WriteLine("Grade: F");
}

int x = 10, y = 20;

// Equality operators
Console.WriteLine($"{x} == {y}: {x == y}");  // Equal to
Console.WriteLine($"{x} != {y}: {x != y}");  // Not equal to

// Relational operators
Console.WriteLine($"{x} < {y}: {x < y}");    // Less than
Console.WriteLine($"{x} > {y}: {x > y}");    // Greater than
Console.WriteLine($"{x} <= {y}: {x <= y}");  // Less than or equal
Console.WriteLine($"{x} >= {y}: {x >= y}");  // Greater than or equal

bool hasLicense = true;
int age = 20;
bool hasInsurance = false;

// AND operator (&&) - both conditions must be true
if (hasLicense && age >= 18)
{
    Console.WriteLine("Can drive legally.");
}

// OR operator (||) - at least one condition must be true
if (hasLicense || age >= 21)
{
    Console.WriteLine("At least one condition is met.");
}

// NOT operator (!) - inverts the boolean value
if (!hasInsurance)
{
    Console.WriteLine("Warning: No insurance coverage!");
}

// Complex logical expressions
if ((hasLicense && age >= 18) && (hasInsurance || age >= 25))
{
    Console.WriteLine("Can rent a car.");
}

char grade = 'B';

switch (grade)
{
    case 'A':
        Console.WriteLine("Excellent!");
        break;
    case 'B':
        Console.WriteLine("Good job!");
        break;
    case 'C':
        Console.WriteLine("Average performance.");
        break;
    case 'D':
        Console.WriteLine("Below average.");
        break;
    case 'F':
        Console.WriteLine("Failed.");
        break;
    default:
        Console.WriteLine("Invalid grade.");
        break;
}

char grade = 'B';

string message = grade switch
{
    'A' => "Excellent!",
    'B' => "Good job!",
    'C' => "Average performance.",
    'D' => "Below average.",
    'F' => "Failed.",
    _ => "Invalid grade."  // Default case
};

Console.WriteLine(message);

// Switch expression with multiple values
string dayType = DateTime.Now.DayOfWeek switch
{
    DayOfWeek.Monday or DayOfWeek.Tuesday or DayOfWeek.Wednesday 
        or DayOfWeek.Thursday or DayOfWeek.Friday => "Weekday",
    DayOfWeek.Saturday or DayOfWeek.Sunday => "Weekend",
    _ => "Unknown"
};

Console.WriteLine($"Today is a {dayType}");

// Basic for loop
for (int i = 1; i <= 5; i++)
{
    Console.WriteLine($"Iteration {i}");
}

// Counting backwards
for (int i = 10; i >= 1; i--)
{
    Console.WriteLine($"Countdown: {i}");
}

// Different increment values
for (int i = 0; i <= 20; i += 2)
{
    Console.WriteLine($"Even number: {i}");
}

// Multiple variables in for loop
for (int i = 0, j = 10; i < 5; i++, j--)
{
    Console.WriteLine($"i = {i}, j = {j}");
}

int count = 1;

while (count <= 5)
{
    Console.WriteLine($"Count: {count}");
    count++;  // Important: increment to avoid infinite loop
}

// Practical example: user input validation
string input;
int number;

Console.Write("Enter a positive number: ");
while (!int.TryParse(Console.ReadLine(), out number) || number <= 0)
{
    Console.Write("Invalid input. Please enter a positive number: ");
}

Console.WriteLine($"You entered: {number}");

int attempts = 0;
string password;

do
{
    Console.Write("Enter password: ");
    password = Console.ReadLine();
    attempts++;
    
    if (password != "secret123")
    {
        Console.WriteLine("Incorrect password. Try again.");
    }
    
} while (password != "secret123" && attempts < 3);

if (password == "secret123")
{
    Console.WriteLine("Access granted!");
}
else
{
    Console.WriteLine("Too many failed attempts. Access denied.");
}

// Array iteration
string[] fruits = { "apple", "banana", "orange", "grape" };

foreach (string fruit in fruits)
{
    Console.WriteLine($"I like {fruit}");
}

// String iteration (strings are collections of characters)
string word = "Hello";
foreach (char letter in word)
{
    Console.WriteLine($"Letter: {letter}");
}

// Working with numbers
int[] numbers = { 2, 4, 6, 8, 10 };
int sum = 0;

foreach (int num in numbers)
{
    sum += num;
}

Console.WriteLine($"Sum of numbers: {sum}");

// Finding a specific number
int[] numbers = { 1, 3, 7, 9, 12, 15, 18 };
int target = 12;
bool found = false;

for (int i = 0; i < numbers.Length; i++)
{
    if (numbers[i] == target)
    {
        Console.WriteLine($"Found {target} at index {i}");
        found = true;
        break;  // Exit the loop early
    }
}

if (!found)
{
    Console.WriteLine($"{target} not found in the array");
}

// Print only even numbers
for (int i = 1; i <= 10; i++)
{
    if (i % 2 != 0)  // If number is odd
    {
        continue;    // Skip this iteration
    }
    Console.WriteLine($"Even number: {i}");
}

// Skip empty strings
string[] words = { "apple", "", "banana", "", "cherry" };

foreach (string word in words)
{
    if (string.IsNullOrEmpty(word))
    {
        continue;  // Skip empty strings
    }
    Console.WriteLine($"Processing: {word}");
}

// Multiplication table
Console.WriteLine("Multiplication Table:");
for (int i = 1; i <= 5; i++)
{
    for (int j = 1; j <= 5; j++)
    {
        Console.Write($"{i * j:D2} ");  // D2 formats as 2-digit number
    }
    Console.WriteLine();  // New line after each row
}

// Pattern printing
Console.WriteLine("\nStar Pattern:");
for (int i = 1; i <= 5; i++)
{
    for (int j = 1; j <= i; j++)
    {
        Console.Write("* ");
    }
    Console.WriteLine();
}

int age = 20;

// Traditional if-else
string status1;
if (age >= 18)
{
    status1 = "Adult";
}
else
{
    status1 = "Minor";
}

// Ternary operator (condition ? true_value : false_value)
string status2 = age >= 18 ? "Adult" : "Minor";

Console.WriteLine($"Status: {status2}");

// Nested ternary operators (use sparingly)
int score = 85;
string grade = score >= 90 ? "A" : 
               score >= 80 ? "B" : 
               score >= 70 ? "C" : 
               score >= 60 ? "D" : "F";

Console.WriteLine($"Grade: {grade}");

Random random = new Random();
int secretNumber = random.Next(1, 101);  // Random number 1-100
int attempts = 0;
int maxAttempts = 7;
bool hasWon = false;

Console.WriteLine("Welcome to the Number Guessing Game!");
Console.WriteLine("I'm thinking of a number between 1 and 100.");

while (attempts < maxAttempts && !hasWon)
{
    Console.Write($"Attempt {attempts + 1}/{maxAttempts}: Enter your guess: ");
    
    if (int.TryParse(Console.ReadLine(), out int guess))
    {
        attempts++;
        
        if (guess == secretNumber)
        {
            Console.WriteLine($"Congratulations! You found the number in {attempts} attempts!");
            hasWon = true;
        }
        else if (guess < secretNumber)
        {
            Console.WriteLine("Too low! Try a higher number.");
        }
        else
        {
            Console.WriteLine("Too high! Try a lower number.");
        }
    }
    else
    {
        Console.WriteLine("Please enter a valid number.");
    }
}

if (!hasWon)
{
    Console.WriteLine($"Game over! The number was {secretNumber}.");
}

bool continueCalculating = true;

while (continueCalculating)
{
    Console.WriteLine("\n=== Simple Calculator ===");
    Console.Write("Enter first number: ");
    
    if (!double.TryParse(Console.ReadLine(), out double num1))
    {
        Console.WriteLine("Invalid number!");
        continue;
    }
    
    Console.Write("Enter operator (+, -, *, /): ");
    string op = Console.ReadLine();
    
    Console.Write("Enter second number: ");
    if (!double.TryParse(Console.ReadLine(), out double num2))
    {
        Console.WriteLine("Invalid number!");
        continue;
    }
    
    double result = op switch
    {
        "+" => num1 + num2,
        "-" => num1 - num2,
        "*" => num1 * num2,
        "/" when num2 != 0 => num1 / num2,
        "/" => double.NaN,  // Division by zero
        _ => double.NaN     // Invalid operator
    };
    
    if (double.IsNaN(result))
    {
        if (op == "/" && num2 == 0)
            Console.WriteLine("Error: Division by zero!");
        else
            Console.WriteLine("Error: Invalid operator!");
    }
    else
    {
        Console.WriteLine($"Result: {num1} {op} {num2} = {result}");
    }
    
    Console.Write("Continue? (y/n): ");
    string answer = Console.ReadLine()?.ToLower();
    continueCalculating = answer == "y" || answer == "yes";
}

Console.WriteLine("Thank you for using the calculator!");