অপারেটরস এবং এক্সপ্রেশনস (Operators & Expressions)

int a = 17, b = 5;

Console.WriteLine($"Add:       {a + b}");   // 22
Console.WriteLine($"Subtract:  {a - b}");   // 12
Console.WriteLine($"Multiply:  {a * b}");   // 85
Console.WriteLine($"Divide:    {a / b}");   // 3  (integer division!)
Console.WriteLine($"Remainder: {a % b}");   // 2  (modulus)

// Watch out: int / int = int (no decimals!)
double exact = (double)a / b;
Console.WriteLine($"Exact div: {exact}");   // 3.4

// Increment & decrement
int score = 0;
score++;        // score is now 1
score += 10;    // score is now 11
score--;        // score is now 10
Console.WriteLine($"Score: {score}");

Add:       22
Subtract:  12
Multiply:  85
Divide:    3
Remainder: 2
Exact div: 3.4
Score: 10

int age = 15;
bool hasTicket = true;

// Comparison operators
Console.WriteLine($"Is teenager: {age >= 13 && age <= 19}");
Console.WriteLine($"Can vote:    {age >= 18}");
Console.WriteLine($"Not a baby:  {age != 1}");

// Logical operators
bool canRide = age >= 12 && hasTicket;
Console.WriteLine($"Can ride:    {canRide}");

bool freeEntry = age < 5 || age > 65;
Console.WriteLine($"Free entry:  {freeEntry}");

bool notAllowed = !hasTicket;
Console.WriteLine($"Blocked:     {notAllowed}");

Is teenager: True
Can vote:    False
Not a baby:  True
Can ride:    True
Free entry:  False
Blocked:     False

// Ternary operator
int temp = 35;
string weather = temp > 30 ? "Hot! Stay inside" : "Nice day!";
Console.WriteLine(weather);

// Null-coalescing ??
string? username = null;
string displayName = username ?? "Anonymous";
Console.WriteLine($"Welcome, {displayName}");

// Null-conditional ?.
string? message = null;
int? length = message?.Length;  // null, not a crash
Console.WriteLine($"Length: {length ?? 0}");

// Pattern matching with 'is'
object mystery = 42;
if (mystery is int number)
{
    Console.WriteLine($"It's a number: {number * 2}");
}

object greeting = "Hello";
if (greeting is string text && text.Length > 3)
{
    Console.WriteLine($"Long greeting: {text}");
}

Hot! Stay inside
Welcome, Anonymous
Length: 0
It's a number: 84
Long greeting: Hello