## 1.1 Hello, World!

Let’s write our very first computer program. Type the following code into the console and press Enter:

cat("Hello, World!")

In the console you should see the following output:

## Hello, World!

That’s it—you just wrote a computer program. A computer program is simply a sequence of instructions that perform a specific task when they are executed (carried out) by the computer. In the above example, there was only one instruction in the sequence: it was the command to reproduce the string “Hello, World” in the console exactly as it is. The name of that command is cat().

Let’s try another small program.

Type the following code into the console and press Enter:

cat(2+2)

In the console you should see the following output:

## 4

We have been using the cat() function so far. Actually you can get output without it. For example, suppose you type:

"Hello, World!"

Then in the console you see:

## [1] "Hello World"

There are quote-marks around the text: that’s not so pretty, but we still get the basic output.

Similarly, you can try:

2 + 2
## [1] 4

Notice that when we don’t use cat() the output begins with a strange [1]. In the next chapter we’ll learn why this happens; for now, just ignore it.