# Integer

This may need some disambiguation information to deal with the computer programming data type.
 Subject classification: this is a mathematics resource.
 Educational level: this is a secondary education resource.
 Educational level: this is a tertiary (university) resource.

The integers are a very fundamental mathematical set on which arithmetic is based. They are the familiar "whole numbers"; that is, they do not include fractional quantities. They include zero and negative whole numbers—the natural numbers are the set that includes only positive whole numbers. That is, the integers are the set ${\displaystyle \dots -3,-2,-1,0,1,2,3,\dots }$.

Mathematicians denote the set of integers with an ornate capital letter: ${\displaystyle \mathbb {I} }$. They are the 2nd item in this hierarchy of types of numbers:

• The "natural numbers"—${\displaystyle \mathbb {N} }$, 0, 1, 2, 3, ...
• The "integers"—${\displaystyle \mathbb {I} }$, positive, negative, and zero
• The "rational numbers"—${\displaystyle \mathbb {Q} }$, or fractions, like 355/113
• The "real numbers"—${\displaystyle \mathbb {R} }$, including irrational numbers
• The "complex numbers"—${\displaystyle \mathbb {C} }$, which give solutions to polynomial equations

## Definition of the integers

Integer represents a set of signed numbers namely Negative numbers , Zero and Positive numbers . Integer is denoted as I . So Negative number is -I and Positive number is +I

${\displaystyle I={-I,0,+I}}$

Where

${\displaystyle I}$ . Integer
${\displaystyle -I}$ . Negative integer
${\displaystyle +I}$ . Positive integer

Negative number is defined as a number has value less than zero

${\displaystyle -I<0}$

Positive number is defined as a number has value greater zero

${\displaystyle +I>0}$

Example Integers of octal base

${\displaystyle I={-9,-8,-7,-6,-5,-4,-3,-2,-1,0,+1,+2,+3,+4,+5,+6,+7,+8,+9}}$

## Mathematical operations

### Differfent integers

${\displaystyle (-I)+0=-I}$
${\displaystyle (+I)+0=+I}$
${\displaystyle (+I)+(-I)=0}$
${\displaystyle (-I)+(+I)=0}$

### Like positive integer

${\displaystyle (+I)+(+I)=+2I}$
${\displaystyle (+I)-(+I)=0}$
${\displaystyle (+I)\times (+I)=I^{2}}$
${\displaystyle (+I)/(+I)=1}$

### Like negative integer

${\displaystyle (-I)+(-I)=-2I}$
${\displaystyle (-I)-(-I)=0}$
${\displaystyle (-I)\times (-I)=I^{2}}$
${\displaystyle (-I)/(-I)=1}$

For all positive x and y, we extend addition to all integers as follows. The value of x+(-y) depends on which is larger, x or y.

If ${\displaystyle x>y}$, ${\displaystyle x+(-y)=x-y}$
If ${\displaystyle x, ${\displaystyle x+(-y)=-(y-x)}$
Also, ${\displaystyle (-y)+x}$ = ${\displaystyle x+(-y)}$, and ${\displaystyle (-x)+(-y)=-(x+y)}$
Finally, ${\displaystyle x+0=0+x=x}$ for all x, positive, negative, or zero.

## Negation

This operator, written "-x", has already been defined for positive numbers. For negative numbers, we define

${\displaystyle -(-x)=x}$. Also, ${\displaystyle -0=0}$.

## Subtraction

We define subtraction for all numbers, positive, negative, or zero, in terms of negation and addition

${\displaystyle x-y=x+(-y)}$

## Multiplication

For negative numbers, we define

${\displaystyle x\times (-y)=-(x\times y)}$
${\displaystyle (-x)\times y=-(x\times y)}$
${\displaystyle 0\times x=x\times 0=0}$
• Ordering: If x and y are both positive numbers:
${\displaystyle -x<-y}$ if and only if ${\displaystyle x>y}$
${\displaystyle -x<0}$, ${\displaystyle -x
${\displaystyle 0>-y}$, ${\displaystyle x>-y}$
In all cases,
${\displaystyle x means x≠y and y > x

From these definitions, we can then prove all the various commutativity, associativity, and distributivity properties, and the trichotomy law. This is left as an exercise.

## Group and ring properties

The integers, with their property of addition, constitute a group. Groups are extremely important objects in mathematics. A group requires a set (the integers), an operation (addition), an "inverse" operation (negation—the natural numbers don't have this, so they are not a group), and an "identity" operation (zero). To be a group, the operation must be associative, a property which the integers satisfy. Also, since addition

Furthermore, the integers have a multiplication operator, satisfying the distributive law, and having a multiplicative identity (1). This makes the integers a ring.