🖥️ How Code Runs: A Beginner’s Guide to What Happens When You Press “Run”

This content originally appeared on DEV Community and was authored by Farhan Shahriar

When I first started learning to code, I wondered: How does my computer know what to do when I write some text and click “Run”?

In this first lesson, I’ll share what I learned — and trust me, understanding this makes you appreciate programming so much more!

Let’s Compare It To Something You Know

Imagine you want to watch a video on your computer. You need video player software — like VLC or Windows Media Player.Or, you want to play a game — you first install the game on your machine.

Running code is very similar.

When you write code, your computer needs a special program that knows how to understand and execute it.For example:

To run C++, you need a compiler like GCC.

To run Java, you need the Java Development Kit (JDK) installed.

If you run your code online, you use an online IDE (like Replit or CodeSandbox). Your code runs on another computer (a server) somewhere in the world. Still, it always needs a machine to run.

What Happens When You Run Code?

Let’s take a simple C++ example:

#include <iostream>
using namespace std;

int main() {
  // Your code goes here
  cout << "Hi...";
  return 0;
}

When you hit Run, your computer does this in two main steps:

1⃣ Compilation Phase

It checks your code line by line.

It finds any errors — like typos or wrong syntax.

2⃣ Execution Phase

It looks for the entry point — in C++ that’s int main().

Then, it starts running your instructions step by step.

Here’s a quick Java example too:

import java.util.*;
import java.lang.*;
import java.io.*;

class FirstCode {
  public static void main(String[] args) throws java.lang.Exception {
    // Your code goes here
  }
}

Again, Java finds the main method and starts executing your logic from there.

So Much Happens Behind the Scenes!

Behind that Run button, there are thousands of lines of code written by other developers — the compiler, the interpreter, the virtual machine. All of this software does the hard work of translating your code into instructions your computer can understand.

If it wasn’t for these tools, we’d have to write those low-level instructions ourselves. Thankfully, people already did that work and packaged it for us!

Does Every Language Run the Same Way?

Most programming languages follow a similar flow:

Check for errors

Find the starting point

Execute the code step by step

The exact details depend on the language (some are compiled, some are interpreted, some use virtual machines). But the big idea stays the same: You write instructions → A special program understands them → Your computer does the work

Key Takeaway

Whenever you write code, you’re actually giving instructions to a machine. The compiler or interpreter is your translator — it converts your words into something the computer’s hardware understands.

So next time you click Run, appreciate the invisible magic happening behind your screen!

Final Thoughts

Understanding how code runs is the first step to becoming a confident programmer.I hope this helped you — follow my journey as I share more beginner-friendly lessons!

This content originally appeared on DEV Community and was authored by Farhan Shahriar