Operators and Expressions in C#

Imagine you're buying snacks from a shop. You add prices, subtract discounts, compare which item is cheaper, and decide whether you have enough money.
Funny thing? Computers do the exact same things, using operators.

Today, you’ll teach C# how to add, compare, and make decisions using expressions, and then build a small program that calculates a bill automatically.

By the end of this lesson, your program will do math for you.

The Project: Simple Bill Calculator

You will build a tiny app that prints the cost of three items and the total bill:

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========================
   SIMPLE BILL
   Item 1: 120
   Item 2: 80
   Item 3: 50
   --------------------
   Total: 250
========================

This mini-project uses arithmetic operators just like real shopping apps. Operators are symbols that tell C# what action to perform.

You’ll use three categories today:

1. Arithmetic Operators

Used for basic math:

• + addition
• - subtraction
• * multiplication
• / division
• % remainder

Example:

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int total = 5 + 3; // total becomes 8

2. Relational Operators

Used to compare values:

• == equal
• != not equal
• > greater than
• < less than
• >= greater or equal
• <= less or equal

Example:

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bool result = 10 > 5; // true

These become powerful when combined with if–else statements later.

3. Logical Operators

Used to connect multiple conditions:

• && AND → both must be true
• || OR → at least one is true
• ! NOT → reverses the value

Example:

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bool ok = (age > 12) && (age < 20);

Increment & Decrement

Sometimes you want to increase or decrease a value by 1.

• x++ → x = x + 1
• x-- → x = x - 1

Example:

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int count = 0;
count++; // becomes 1

This is very useful in loops (coming soon!).

Operator Precedence

Just like math, some operations happen before others.

Example:

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int x = 5 + 3 * 2;  // result is 11, not 16

Because multiplication (*) happens before addition (+). If you want to control the order, use parentheses:

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int y = (5 + 3) * 2;  // result is 16

Let’s Build the Simple Bill Calculator

Here is the full program:

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using System;

class Program
{
    static void Main()
    {
        int item1 = 120;
        int item2 = 80;
        int item3 = 50;

        int total = item1 + item2 + item3;

        Console.WriteLine("========================");
        Console.WriteLine("   SIMPLE BILL");
        Console.WriteLine($"   Item 1: {item1}");
        Console.WriteLine($"   Item 2: {item2}");
        Console.WriteLine($"   Item 3: {item3}");
        Console.WriteLine("   --------------------");
        Console.WriteLine($"   Total: {total}");
        Console.WriteLine("========================");
    }
}

This is your first “math-powered” C# program.

How It Works

• Three variables store item prices.
• The expression item1 + item2 + item3 calculates the total automatically.
• String interpolation prints neat, readable output.

If you change one price, the total updates instantly, no extra work!

Run it in the DevsCall AI Code Runner to see it in action.

Learn Together with AI

Try prompts like:

• “Change the bill calculator to include a 10% discount.”
• “Add tax calculation to my C# bill program.”
• “Explain operator precedence with more examples.”
• “Write a version where user enters the item prices.”

AI can help you build more advanced calculators step-by-step.

Practice Time

Create a program that:

• Stores the prices of 4 grocery items
• Calculates the total price
• Prints everything in this format:

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========================
   GROCERY BILL
   Apple: 100
   Milk: 180
   Bread: 140
   Eggs: 200
   --------------------
   Total: 620
========================

Use arithmetic operators to compute the total.

Example Solution

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using System;

class Program
{
    static void Main()
    {
        int apple = 100;
        int milk = 180;
        int bread = 140;
        int eggs = 200;

        int total = apple + milk + bread + eggs;

        Console.WriteLine("========================");
        Console.WriteLine("   GROCERY BILL");
        Console.WriteLine($"   Apple: {apple}");
        Console.WriteLine($"   Milk: {milk}");
        Console.WriteLine($"   Bread: {bread}");
        Console.WriteLine($"   Eggs: {eggs}");
        Console.WriteLine("   --------------------");
        Console.WriteLine($"   Total: {total}");
        Console.WriteLine("========================");
    }
}

If your output matches, you’ve mastered expressions and operators!