2. Real-world story

At Practo appointment booking API, engineers use Loops to process every line item in an order or every row in a CSV import. This code shows the same pattern you will see in code reviews — simplified for learning, but structurally similar to production services deployed to Azure or on-prem IIS/Kestrel.

3. Problem without this concept

If you ignore Loops, this is what teams struggle with:

• Copy-pasted code for each row → unmaintainable reports
• Infinite loops freezing console apps

4. Definition

Loops is a core part of C# and .NET development. In plain terms: it helps you process every line item in an order or every row in a CSV import.

5. Why do we need it?

You will see Loops in console apps, Web APIs, background workers, and unit tests. Skipping it makes later modules (OOP, async, collections) much harder. Every day — syntax, types, and control flow appear in every file you write.

6. Where is it used?

• Banking transfer validation
• E-commerce price calculators
• LMS quiz scoring
• Banking apps use if/else for transfer limits; e-commerce uses loops for cart line items.
• Wrong data types cause money rounding bugs — decimal for currency, int for counts.

7. How it works

• Read the example top to bottom.
• Each line connects to Loops.
• Run it with dotnet run, then change one value and predict the output before you save.

8. Syntax

Core syntax pattern for Loops:

foreach (var item in collection)
{
    // process item
}

9. Beginner example

Copy into a console project (dotnet new console → dotnet run).

var orderIds = new[] { 101, 102, 103, 104 };
decimal total = 0;

foreach (var id in orderIds)
{
    decimal lineTotal = id * 10.5m; // simplified
    total += lineTotal;
    Console.WriteLine($"Order {id}: ₹{lineTotal}");
}
Console.WriteLine($"Grand total: ₹{total}");

Line-by-line

10. Real project example

At Practo appointment booking API, engineers use Loops to process every line item in an order or every row in a CSV import. This code shows the same pattern you will see in code reviews — simplified for learning, but structurally similar to production services deployed to Azure or on-prem IIS/Kestrel.

Production-style C#

// Practo appointment booking API
// Uses Loops to process every line item in an order or every row in a CSV import
var orderIds = new[] { 101, 102, 103, 104 };
decimal total = 0;

foreach (var id in orderIds)
{
    decimal lineTotal = id * 10.5m; // simplified
    total += lineTotal;
    Console.WriteLine($"Order {id}: ₹{lineTotal}");
}
Console.WriteLine($"Grand total: ₹{total}");

Why teams use this: Teams that master Loops ship fewer production incidents and pass code review faster on Practo-scale systems.

11. Visual understanding

Input (user, file, API)
        │
        ▼
   Loops logic in C#
        │
        ▼
   Output (console, HTTP response, file)

12. Internal working

• Roslyn compiler checks syntax and types before your program runs.
• CLR executes IL and provides services (GC, exceptions, threading).
• For this lesson, focus on behavior first — runtime details matter more as apps grow.

13. Advantages

• Readable code that new team members can follow
• Compiler catches many mistakes before deploy
• Huge .NET job market in India and worldwide

14. Disadvantages

• Takes time to learn if you skip fundamentals
• Overusing advanced features too early adds complexity

15. Best practices

• Use meaningful names — `transferAmount` not `x`
• Run `dotnet format` or EditorConfig for consistent style
• Commit small examples to Git from lesson one

16. Common mistakes

• Copy-pasting without typing — your fingers need to remember Loops syntax.
• Skipping error messages when the compiler fails — the red text usually tells you exactly what to fix.

17. Interview questions

Do this on your computer

1. Open Visual Studio or run dotnet new console -n LearnLoops.
2. Paste the lesson example into Program.cs (or a new file).
3. Run the program and confirm the output matches your expectation.
4. Read the real-world section and name which part of a banking or e-commerce API would use this topic.
5. Change one line (amount, loop bound, or method name) and run again.
6. Read the real-world section and identify which layer (API, service, domain) uses this topic.
7. Run dotnet build and dotnet run locally — confirm output.
8. Change one value and predict the result before saving.

Experiments — try changing this

• Change a number or string in the example and run again — predict output first.
• Introduce a deliberate error (remove a semicolon) and read the compiler message.
• Add one more item to the collection and confirm the loop runs one extra time.

18. Summary

• Loops is used to process every line item in an order or every row in a CSV import.
• Practice by editing the example yourself.
• Move to the next lesson when you can explain this topic in your own words.