C# Operators and Expressions

In C#, operators are special symbols that perform operations on variables or values. With these symbols, you can do mathematical calculations, compare two values, build logical conditions, or quickly assign a value to a variable. Structures formed by combining operators are called expressions. Expressions are the fundamental building blocks that drive program flow and produce results.

Assignment Operator (=)

Used to assign a value to a variable.

int x = 5;
string message = "Hello";
x = 10;

Here, the value 5 is assigned to the variable x of type int, and the value "Hello" is assigned to the variable message of type string. Later, the value 10 is assigned to x.

Arithmetic Operators

Arithmetic operators are used to perform numeric operations in C#. They handle basic math such as addition, subtraction, multiplication, division, and modulus (remainder).

Example:

int a = 15;
int b = 4;

Console.WriteLine(a + b); // 19
Console.WriteLine(a / b); // 3
Console.WriteLine(a % b); // 3

Comparison Operators

Comparison operators in C# are used to compare two values. The result of these operations is always of type bool.

Example:

int a = 7;
int b = 10;

bool result1 = (a < b);     // true
bool result2 = (a == b);    // false

Console.WriteLine(result1); // true
Console.WriteLine(result2); // false

Logical Operators

Used to combine conditions. These conditions are of type bool. They perform the logical operations and, or, and not.

Operators are used as follows:

For example, if variable x is less than 5 and variable y is greater than 10, you can write the condition as:

bool crit = x < 5 && y > 10;

A simple example that states the user can drive if they are over 18 and have a driver’s license:

using System;

class Program
{
    static void Main()
    {
        Console.Write("Enter your age: ");
        int age = int.Parse(Console.ReadLine());

        Console.Write("Do you have a driver's license? (Y/N): ");
        string answer = Console.ReadLine().ToUpper();

        bool hasLicense = (answer == "Y");

        if (age >= 18 && hasLicense)
        {
            Console.WriteLine("You can drive a car.");
        }
        else
        {
            Console.WriteLine("You cannot drive a car.");
        }
    }
}

Compound Assignment Operators

Combine assignment with arithmetic. For example, add 5 to a number, subtract 2, or multiply it by 6.

Increment and Decrement Operators

Used to increase or decrease a number by 1.

int x = 5;

x++; // 6
x--; // 5

Prefix vs. Postfix:

int a = 5;
Console.WriteLine(++a); // 6 (increment first, then print)
Console.WriteLine(a++); // 6 (print first, then increment → a=7)

Ternary Operator (?:)

A short form of if-else. Conditionally selects one of two values.

using System;

class Program
{
    static void Main()
    {
        Console.Write("Enter a number: ");
        int num = int.Parse(Console.ReadLine());

        string result = (num % 2 == 0) 
            ? "The number you entered is even." 
            : "The number you entered is odd.";

        Console.WriteLine(result);
    }
}

• The number is read with Console.ReadLine().
• Converted from string to int with int.Parse.
• The ternary (?:) checks num % 2 == 0.
• The result message is printed to the screen.

Null-Coalescing Operators (?? and ??=)

In C#, null indicates that a variable does not reference any value. In other words, the variable is defined but contains no value. This commonly appears with string or class (reference type) variables.

Sometimes we want to assign a default value instead of a null one. This is where the null-coalescing operators come into play:

Example 1: Using ??

string name = null;
string result = name ?? "Anonymous";

Console.WriteLine(result);

Example 2: Using ??=

string name = null;
name ??= "Unknown";

Console.WriteLine(name); // Unknown

Example (Shopping Cart)

using System;
using System.Globalization;

class Program
{
    static void Main()
    {
        // Input culture: reduce dot/comma issues
        CultureInfo.CurrentCulture = CultureInfo.InvariantCulture;

        // 1) Get user inputs one after another
        Console.Write("Name (you may leave it blank): ");
        string name = Console.ReadLine();
        name = string.IsNullOrWhiteSpace(name) ? null : name.Trim();
        name ??= "Guest"; // (??=) assign default name if null

        Console.Write("City (you may leave it blank): ");
        string city = Console.ReadLine();
        city = string.IsNullOrWhiteSpace(city) ? null : city.Trim();
        string cityInfo = city ?? "Unknown City"; // (??) value to display if null

        Console.Write("Cart total (e.g., 749.90): ");
        double cartTotal = double.Parse(Console.ReadLine());

        Console.Write("Are you a member? (Y/N): ");
        bool isMember = Console.ReadLine().Trim().ToUpper() == "Y";

        Console.Write("Coupon code (you may leave it blank): ");
        string coupon = Console.ReadLine();
        coupon = string.IsNullOrWhiteSpace(coupon) ? null : coupon.Trim().ToUpper();

        Console.Write("Would you like express shipping? (Y/N): ");
        bool express = Console.ReadLine().Trim().ToUpper() == "Y";

        // 2) Business rules and operators

        // Arithmetic: VAT, discount, shipping, total
        const double VatRate = 0.20;          // 20% VAT
        const double MemberDisc1 = 0.05;      // 5% if member
        const double MemberDisc2 = 0.10;      // 10% if member and cart >= 500
        const double CouponDisc = 0.10;       // +10% if coupon is "INDIRIM10"
        const double MaxDiscount = 0.25;      // Discount cap at 25%
        const double StdShipping = 19.90;
        const double ExpressShipping = 49.90;
        const double FreeShippingThreshold = 300.0;

        // Comparison + logical: determine discount rate
        double discountRate = isMember && cartTotal >= 500
            ? MemberDisc2
            : (isMember ? MemberDisc1 : 0.0); // (?:) ternary

        // Logical: coupon check (OR)
        if (coupon == "DISCOUNT10" || coupon == "CODE10")
            discountRate += CouponDisc;       // Compound assignment (+=)

        // Apply cap
        discountRate = Math.Min(discountRate, MaxDiscount);

        // Calculate discount and VAT
        double discountAmount = cartTotal * discountRate;  // (*)
        double subTotal      = cartTotal - discountAmount; // (-)
        double vat           = subTotal * VatRate;         // (*)

        // Shipping: express? otherwise check free-shipping threshold
        double shipping = express
            ? ExpressShipping
            : (subTotal >= FreeShippingThreshold ? 0.0 : StdShipping);

        // Grand total
        double grandTotal = subTotal + vat;               // (+)
        grandTotal += shipping;                           // Compound assignment (+=)

        // 3) Summary output
        Console.WriteLine();
        Console.WriteLine("— Payment Summary —");
        Console.WriteLine($"Customer     : {name} ({cityInfo})");
        Console.WriteLine($"Cart         : {cartTotal:0.00} £");
        Console.WriteLine($"Discount %   : {(discountRate * 100):0}%  (-{discountAmount:0.00} £)");
        Console.WriteLine($"Subtotal     : {subTotal:0.00} £");
        Console.WriteLine($"VAT (20%)    : {vat:0.00} £");
        Console.WriteLine($"Shipping     : {shipping:0.00} £ {(express ? "(Express)" : "(Standard)")}");
        Console.WriteLine($"Grand Total  : {grandTotal:0.00} £");

        // Extra logical example: invoice note
        bool highCart = grandTotal >= 1000.0;
        Console.WriteLine(highCart && isMember
            ? "Note: You earned extra points for your high-value order."
            : "Note: Become a member to benefit from extra discounts.");
    }
}

With this example, you can try a console application that combines the topics above.

The application output will look like the screenshot above.