Data types

Facts:
In Computer Science, the kind of information is call type

Example of different types of information:

Numerical information, such as:
- Age
- Pay (salary)
- etc.
Alpha-numerical (textual) information, such as:
- Plain text (like a book)
- Structured text (e.g., dictionary)
Logic information, such as:
- Married ?
- Registered ?
- etc
Miscellaneous information, such as:
- Gender information
- Marital information
- etc.

Values

Example 1:

Necessary for information: type and value

For information to be meaningful, it requires:
Both components are necessarity
Without either component, we cannot make sense of the data

Example:

If I tell you the value 22, without telling you that it is the "Age of John", you have no idea what 22 mean.
If I tell you "This is the age of John", without telling you the value, you have no idea how old John is.

Variables

Variable in Computer Science

A variable in Computer Science is a memory cell
A memory cell can store a value
(Remember the Store and Recall function of a calculator ? That works like a memory cell)

Real-life analogy of a variable

A variable (in Computer Science) is like a piece of paper with a tag attached to it.
You can only write one (binary) number on the piece of paper.
You can erase the number and write a new number on the paper; but you can never write more than one number on the paper at any time.

Data types built into a computer

Built-in data types

Examples:

The integer number 1 is represented inside the computer by the byte (= 8 bits) 00000001
The integer number 2 is represented inside the computer by the byte (= 8 bits) 00000010
The computer also knows how to add, subtract, multiply and divide binary numbers.

We don't need to learn about how the computer does it in this course. It will be explained in other courses.

Integers and floating point numbers of different lengths

Recall that:

The smallest memory element in a computer RAM memory is a byte (= 8 bits)
The computer can combine adjacent bytes (memory cells) and use it as a larger memory cell

Practically speaking, the integer value 1 can be represented inside the computer using:
There is a trade-off between

Data types in a programming language

Althought the computer can only work with 2 data types (integers and floating numbers), a programming language can uses these two data types to represent any number of data types
All it takes is a bit of imagination
The way a programming language represents a new data type is as follows:
(Context: remember the example of "you is a word" and "you are a student" ?)
The context information is called type information in Computer Science

Very important facts:

Every value stored used inside a program is a (binary) number
Every value stored used inside a program has a type
The type information provides the context to interprete the given value

Example:

The Java programming language
- In this course, we will be studying the programming language named Java
- It is important to understand
Common data types that are pre-defined in a programming language
- Every modern programming language provides the following pre-defined data types
- The names of the built-in data types as usually:
The int data type
- Recall that a computer can process 2 types of data representations:
- The int data type in a programming language uses the same representation as the integers in
The int data type
- Example: how a programming language represent logic information
  In other words:

Logic value	Value used to encode the lo/types.html gic value
true	1 (integer)
false	0 (integer)