# Input, processing, and output

[Programming guides](README.md)

Many programs do three things: receive information, do something with it, and show a result. These parts are called **input**, **processing**, and **output**.

Input can come from a question, a key press, a saved value, or a sensor. Output can be a message, a picture, or a sound. A program does not always need a person to type something.

## A smoothie machine

Fruit goes into a blender, the blender mixes it, and a smoothie comes out. In a greeting program, a nickname goes in, some words are joined together, and a greeting comes out.

Unlike the blender, the program can keep the original input while making its result. Creating a greeting does not erase the nickname.

## Follow the information

Run this with an input-capable host, such as the Pliro [IDE](../concepts/ide.md). Use the pretend nickname `Nova`; you do not need to enter your real name.

```pliro
# language: en
let nickname = ask("Choose a pretend nickname:")
let greeting = "Hello, " + nickname + "!"
say greeting
```

`ask` supplies the input as text. The `+` signs join pieces of text: that is the processing. `say` displays the result: that is the output. The variable `greeting` remembers the joined text.

## Predict, then run

Which message should appear after you enter `Nova`?

```text
Hello, Nova!
```

The space after the comma comes from `"Hello, "`. Pliro does not guess where a sentence needs spaces.

## Your challenge

Make the program say goodbye using the same nickname. You do not need to ask twice. Then decide what greeting you want when somebody submits an empty answer.

## A common mistake

A reply to `ask` is text, even if somebody types digits. The text `"12"` and the number `12` are different kinds of value. For a question that requires a number, use [askNumber](../builtins/askNumber.md) with suitable limits.

If the program waits for a reply, it has not necessarily crashed. Look for its question and answer it, or use Stop if you want to end the run.

## Where next?

[Questions and keyboard input](input.md) · [Unusual inputs](unusual-inputs.md) · [Sharing safely](safe-sharing.md)