Commands and the first program in Kotlin

1. Getting to know commands

If you ever imagined a programmer’s work as something incomprehensible and mysterious, it’s time to bust that myth! Programming is not a secret art, but an awesome and very interesting job. And you’re about to see that for yourself.

Computer programs are written using programming languages—special rules and words that computers understand. Today you’ll get acquainted with the Kotlin language: you’ll write your first program, learn what commands are, and make the computer obey you (as much as it feels like, of course). 😅

A program is a set (list) of commands. First, the first command is executed, then the second, third, and so on. When all commands are executed, the program ends.

    flowchart LR
    A([🚀 Program starts]) --> B

    B[📋 Command 1]
    B --> C[📋 Command 2]
    C --> D[📋 ...]
    D --> E([✅ Program ends])

    style A fill:#4CAF50,color:#fff,stroke:#388E3C
    style E fill:#2196F3,color:#fff,stroke:#1565C0
    style B fill:#FFF9C4,stroke:#F9A825
    style C fill:#FFF9C4,stroke:#F9A825
    style D fill:#FFF9C4,stroke:#F9A825

Which exact commands can appear in the command list depends on who executes them—more precisely, on which commands the executor knows (and understands). You can give a dog the command “Sit,” “Speak,” a cat—“Shoo,” a person—“Stop!”, and a robot—“Work!”. 👨‍💻

A command is a simple instruction to the computer: do this! The most important thing is that the computer does exactly what you told it to do, not what you meant. 😆 At least until artificial intelligence grows up, of course.

The set of commands in the Kotlin language is quite extensive. For example, this command can print a message to the screen:

println("Robot is a friend of humans")

This command tells the computer: “Print the text "Robot is a friend of humans" on the screen.”

If you want the computer to print your phrase three times, give it the command several times.

A program of three commands:

println("Robot is a friend of humans")
println("Robot is a friend of humans")
println("Robot is a friend of humans")

As a result, the computer will print the phrase 3 times. It’s that simple. 😎

2. The main() function

Your program, depending on its size, can consist of one or several files. And each file contains commands grouped into functions. A minimal Kotlin program must have at least one function where its execution starts. This function is called main().

The main() function is the entry point to your program. Code execution always starts from it. In Kotlin, a minimal program can consist of a single main() function, which may not contain any commands at all.

A minimal Kotlin program looks like this:

fun main() {   
}

As you can see, the main() function in this example doesn’t contain a single command. But it’s still a fully functional (though minimal) program. Its appearance is always the same:

fun main() {
   // The function code is written here
}

This approach makes Kotlin more accessible to beginners, letting you focus on the program’s logic rather than extra boilerplate around your first program.

3. Program execution order

Your program simply executes all commands from top to bottom, line by line. When the commands run out, the program ends.

Let’s look at a simple example:

fun main() {
   println("Hello everyone!")
   println("Today we’re learning to write in Kotlin!")
}

The output of this code will be:

Hello everyone!
Today we’re learning to write in Kotlin!

Add a couple more lines, and the computer will obediently print them to the screen. It’s very hardworking, but modest—it won’t print anything extra.

4. Writing and running your first program

Why put off a good thing until later? It’s time to move from theory to practice! Let’s write the first program in Kotlin.

Step 1: open WebIDE

Open WebIDE and write a program that prints the message "It’s cool to be a programmer! 😎" on the screen.

You should have a file named Solution.kt open.

Step 2: write the following code there

You can include emojis too—Kotlin supports them perfectly! 🥰

fun main() {
   println("It’s cool to be a programmer!😎")
}

Step 3: submit the program for checking

At the top of the WebIDE panel, you’ll have a "Check" button. Click it.

In the Output window, you should see:

It’s cool to be a programmer!😎

If you did everything correctly, the server will accept your solution and congratulate you. 😎

You’ve just written and successfully submitted your first program in Kotlin. Nice, right? Now you’re a real programmer (well, at least one step closer to earning that title). 😇