# Variables & Data
A variable holds information, numbers, words: data. It gives the programmer the ability to store, manipulate, retrieve, and output information.\
\
Some programming languages are ["Typed" languages](https://hackernoon.com/i-finally-understand-static-vs-dynamic-typing-and-you-will-too-ad0c2bd0acc7). They have a specific *kind* of variable, depending on what you want to do. This is important because different types of variables require different amounts of memory (RAM) in the computer. C++ and Java are strongly (or statically) typed languages. \
\
Here are a few variable types, the amount of memory they require, and their limitations:
| DATA TYPE | CONTENTS | SIZE (IN BYTES) | RANGE |
| ----------------- | --------------------------------- | --------------- | ------------------------------------------------ |
| short int | Whole Numbers | 2 | -32,768 to 32,767 |
| int | Whole Numbers | 4 | -2,147,483,648 to 2,147,483,647 |
| unsigned int | Positive Whole Numbers | 4 | 0 to 2,147,483,647 |
| char | Single Character | 1 | -128 to 127 |
| float | Numbers, including decimal values | 4 | $$17\times10^{-38} \text{ to }1.7\times10^{38}$$ |
| bool (or boolean) | True or False | 1 | 0 to 1 |
| String | Text\* | Varies | Char\[] array |
*\*Strings are not a primitive data type, they are an array of chars or a special type called an **object**.*\
More on data types:\
**C++:** \
**Java:** \
**Javascript:**
{% hint style="info" %}
When creating a variable in *strongly typed* languages, the programmer needs to know exactly what the variable will be holding. The micro-management of memory and data types is what makes C++ such a strong language for things like video games.
{% endhint %}
**Javascript** is [not a strongly typed language](http://exploringjs.com/impatient-js/ch_values.html#whats-a-type). Neither is Python, Ruby, Perl, or Lua. They are what we call [*dynamically typed*](https://stackoverflow.com/questions/1517582/what-is-the-difference-between-statically-typed-and-dynamically-typed-languages). They can transition between variable types and do not require the programmer to declare what type of variable is required. The interpreter will even convert a character to a number and back again, as needed.
{% tabs %}
{% tab title="Javascript" %}
Javascript uses a keyword to create (declare) a variable. \
There are three different keywords, each with a special meaning:
```javascript
// can hold all sorts of data and is globally scoped (more on scope later)
var myVariable;
// can hold all sorts of data and is locally or block scoped
let myOtherVariable;
// can hold all sorts of data but that data cannot change (or shouldn't, at least)
const myConstant;
```
***For this course, it would be best if we use*** `let` ***as often as possible.***
I don't expect everyone to read it, but [here is a great chapter](http://eloquentjavascript.net/01_values.html) on variables in JS.
{% hint style="warning" %}
The "const" declaration in JS does not necessarily mean the variable cannot change. This is a strange property of Javascript and is above the scope of this course. If you'd like to learn more, you can search "javascript immutable const".
{% endhint %}
{% endtab %}
{% tab title="Python" %}
Python is a dynamically typed language. You don't even need to put a declaration at all before a variable. You can simply give a new variable name and Python will open memory for it.
```python
a = 123 # integer
b = 123L # long integer
pi = 3.14 # double float
myString = "hello" # string
myList = [0,1,2] # list
myTuple = (0,1,2) # tuple
myFile = open(‘hello.py’, ‘r’) # file
```
{% endtab %}
{% tab title="C++" %}
C++ is a very strongly or statically typed language. It even has something called *pointers* which point to (reference) an area in memory instead of a value. Kind of like pointing to your locker instead of seeing what is in your locker.
{% code title="" %}
```cpp
int myInt;
int * myPointer; // A pointer to an int
float myBigNumber;
bool theSkyIsBlue = true; // You can initialize variables as you declare them
char aSingleLetter;
char myWord[] = { 'H', 'e', 'l', 'l', 'o', '\0' }; // String
char myOtherWord[] = "Hello";
```
{% endcode %}
{% endtab %}
{% tab title="Java" %}
Java is extremely similar to C++ in terms of variable declarations and options. It is a strongly (or statically) typed language.
```java
int numberOfDays = 7;
byte nextInStream;
short hour;
long totalNumberOfStars;
float reactionTime;
double itemPrice;
String helloWorld = "Hello World!";
String newStringOnHeap = new String("Goodbye Sleep!");
```
{% hint style="info" %}
Java is a bit different than C++ in that it has a **`String`** variable (array of chars). \
A String is **more** than just a variable - it is something called an **`Object`**. You'll see in the code above, there are two ways to declare a String. That's because there is something called a **`Heap`** in Java. More on that in Grade 12!
{% endhint %}
{% endtab %}
{% endtabs %}
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