We have studied various types of numbers till now. These numbers are used for counting and for various other practical purposes.

Types of Numbers 
    1.     Natural Numbers    2.     Whole Numbers     3.     Integers

1.    Natural Numbers: All numbers which are used for counting are called natural numbers. 
      {1, 2, 3,......} etc. are examples of natural numbers. The set of natural numbers is denoted by N, 
      i.e. N = {1, 2, 3,.......}

2.    Whole Numbers: All natural numbers including zero are called whole numbers. {0, 1, 2 3,....} etc. are examples of whole numbers. The set of whole numbers is denoted by W, i.e. W = {0,1,2,3......}

3    Integers: All whole numbers as well as their negatives are called integers. {...–3, –2, –1, 0, 1, 2, 3,...} are examples of integers. The set of integers is denoted by I, i.e. I = {...–3, –2, –1, 0, 1, 2, 3,...}

    Important Points : 
    (i)     All natural numbers are whole numbers but all whole numbers are not natural numbers.
    (ii)     Zero(0) is an integer which is neither a positive number nor a negative number.
    (iii)     When zero(0)  is added to any other number, it gives the same number.