Data types

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The simplest primitive data types

Every high-level computer programming language has a built-in understanding of a few different types of data. The differentiation in how a computer "understands" data is, of course, different from how humans think about data. Some common data types are outlined below.


Simple numbers with no decimal place.


  • 4
  • 666
  • -2

Floating point numbers

Numbers with decimal points.


  • 12.2
  • 3.14159
  • 1.0


Regular text is usually represented by programming languages as a "string of characters" or "string" for short.

Most programming languages require that quotation marks be placed around string literals to differentiate them from other keywords in the language. Whether to use double or single quotes for this is dependent on which language you are using.


  • "money"
  • "4" #note that most languages will treat this as a string, not an int because of the quotes
  • "12.2" #note that most languages will treat this as a string, not a float because of the quotes

See more on Strings


Boolean values are those propositions which the programming languages understands to be either true or false.

Examples of Boolean values in Python:

  • True
  • False

Examples of Boolean values in Java:

  • true
  • false

See more on Boolean logic

Aggregate data structures

Some data structures allow you to group together a bunch of different pieces of data into a single aggregate data structure. These are a bit more "high-level".

Lists and arrays

Lists, also known as arrays, are groups of single values.

  • e.g. "money", "wealth", and "peanut butter"

Dictionaries, associative arrays, and hash maps

Dictionaries, associative arrays, and hash tables, are all data structures that hold a group of key/value pairs.

  • e.g. "my_name": "Inego Montoya", "reason_here": "to kill your father"

Incompatibilities among data types

When trying to perform operations on values of multiple data types, it is not uncommon to find incompatibilities among the data types. Each high-level programming language has its own limitations on how different data types can be mixed and matched in operations.

Python examples

Example of an error:

x = "my favorite number " #a string
y = 4 #an int
z = x + y #an error!  you cannot add a string to an int

Example of a potential solution

x = "my favorite number " #a string
y = 4 #an int
z = x + str(y) #fine!  the int was converted to a string before adding

Converting among data types

Often it is useful to translate a value from one data type into another data type. Each high-level programming language has its own techniques for how to convert data of one type to data of another type.

Python examples

Imagine you have a variable x

x = "4"

Python built-in functions:

  • int(x) – converts a float or string to an integer
  • float(x) – converts an integer or string to a float
  • str(x) – converts an integer or float to a string
  • bool(x) - converts various data types to a boolean equivalent
  • list(x) - converts any data type to a list

Code examples

x = input("What's your lucky number today?")

y = int(x) * 10

msg = "Your lucky number times ten is " + str(y)


If you're not sure what data type a given value is, find out. Each high-level programming language has its own techniques for introspection, or discovering information about the system and the data stored in the system.

Python examples

  • type(x) – determines what type a given piece of data is
  • dir(__builtins__) #shows you a list of Python’s built-in functions
  • print(input.__doc__) #shows you the input() function’s (or any other function’s) usage documentation
  • help(input) #shows you the Python help for the input() function (or any other function)

Code examples

if type("a haircut") == str:

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