Source Code

When you write a C# program, you type text into a file — for example Program.cs. This human-readable text is called "source code". It consists of words and symbols that follow strict, well-defined rules, but is still readable to you.

using System;

class Program
{
    static void Main()
    {
        Console.WriteLine("Hello, World!");
    }
}

A computer, however, cannot execute this text directly. A processor only understands "machine language" — tiny electrical signals represented as zeros and ones. Source code is therefore an intermediate stage: understandable for humans, but not yet directly executable by the hardware.

A computer processor can execute C# source code directly, without translating it first.

C# source code is always saved in files with the extension ".cs". Unlike some other languages, C# does not require the file name to match the name of a class inside it — you could name the file above "Greeting.cs" and it would still work fine, as long as it's part of the project.

C# source code files always have the file extension ____.

In summary: source code is the starting point of every C# program. It is the text that you, as a developer, write, read, and edit yourself. Later — with the help of another tool — this text becomes something the computer can actually execute. You will learn about that tool in the next lesson.

What best describes "source code"?