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Integral numerical information

Previously discussed

Recall that:

A byte is a memory cell consisting of 8 switches and can store a binary number (See: click here )
Although the computer stores binary numbers, we can interprete then as decimal number through a conversion operation:
The computer can combine adjacent bytes in the RAM memory to form larger memory cells
Although a computer memory can only store numbers, we can use an encoding scheme to represent any kind of information
(E.g.: marital status information: 0 = single, 1 = married, and so on...
gender information: 0 = male, 1 = female)
We must have context information to interprete a number that is stored in the RAM memory
(E.g., we cannot interpret the number 0 stored in RAM meory unless we know kind of information it is.)

Storing information inside a computer
- A Java computer program uses variables to store information
- There are different kinds (types) of variables
- In this webnote, we will study the integer variables

Variables (in general)

Variable in Java

A variable in a computer program is in fact a memory cell
A memory cell can store a number
Each variable in Java has a data type
The data type allows the computer program to use the approriate encoding (interpretation) scheme to interprete the number stored in the variable

Analogy of a variable

A variable (in Computer Science) is like a piece of paper with a tag attached to it.
The tag represents the data type of the variable (the value of the tag cannot be changed)
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.

Integer variable

An integer variable is a variable that:

uses 4 consecutive bytes of memory as a single 32 bit memory cell
uses the binary number system as encoding scheme
It can hold an integer number of about 10 (decimal) digits

Every variable in Java must be defined
Also, you must use the correct syntax construct to write a variable definition

Syntax to define an integer variable:

int NameOfVariable ;

Notes:

The keyword int announces the variable definition clause
The NameOfVariable is an identifier which is the name of the variable.
The variable definition clause is must be ended with a semi-colon ";"

Example:

public class Var01 { public static void main(String[] args) { int x; // Define integer variable with name "x" System.out.println("Hello Class"); System.out.println(" The variable x contains this number:"); System.out.println(x); // Print varibale "x" } }

Notes:

The name of the Java program is Var01
Therefore, the UNIX filename that contain this Java program must be: Var01.java
The statement "System.out.println(x);" will print the content of the variable x to the terminal

Example Program: (Demo above code)

Prog file: click here

If you compile the program, you will get an error:

Var01.java:11: variable x might not have been initialized System.out.println(x); // Print the content in variable "x" ^

This is because the variable x does not have a value yet.

Update the value stored in a variable

Assignment statement:

Syntax of an assignment statement:

VariableName = Value ;

Notes:

The symbol = is used to tell the computer to assigne some value to a variable
The symbol = is called the assignment operator in Java
The item on left-hand-side of the = operator is the receiving variable
The item on right-hand-side of the = operator is the value that is assigned to the receiving variable
The assignment statement must be ended with a semi-colon ";"

Example:

public class Var02 { public static void main(String[] args) { int x; // Define integer variable with name "x" x = 12345; // Assign 12345 to x System.out.println("Hello Class"); System.out.println(" The variable x contains this number:"); System.out.println(x); // Print varibale "x" } }

Notes:

The name of the Java program is now Var02
Therefore, the UNIX filename that contain this Java program must be: Var02.java
(I will not make this comment anymore from this point on...)

Example Program: (Demo above code)
- Prog file: click here
How to run the program:
Output:

Integer operators

Integer operators are arithmetic operators that manipulate (operate on) integer values
Most of the integer arithmetic operators should look familiar

Integer arithmetic operators:

Operator symbol	Operation
`+`	addition
`-`	subtraction
*``**	multiplication
`/`	*compute the quotient* of a division**
`%`	*compute the remainder* of a division**

Example:

Result of the integer operation 5 + 3 is 8 Result of the integer operation 5 - 3 is 2 Result of the integer operation 5 * 3 is 15 Result of the integer operation 5 / 3 is 1 (quotient !) Result of the integer operation 5 % 3 is 2 (remainder !)

Integer expressions
- An integer expression is a (legal) combination of
Section
Section
- Locations in a Java program where you can define variables:
  Schematically:
- Warning:

Data types built into a computer

Types of data:

Built-in data types

Every computer has 2 built-in types:
In other words:

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:

We will write the type next to the value in the examples
0 (integer) represents 0 (numeric)
1 (integer) represents 1 (numeric)
0 (logical) represents false
1 (logical) represents true

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)