Both variables and the constants may have different types of values. In C language, different forms of data are categorized into a few abstract data types. For example, suppose you are asked to keep the record of the number of passengers in a bus. A variable say N, which is used to denote this number, will have value in whole numbers because the number of passengers cannot be a fractional number. Similarly, for number of students in a class, number of apples in a basket, number of pages in a book, or number of houses in a colony, etc., the values must be in whole numbers. Whole numbers form a category called integers. In C language, this type is coded as int, a short form for integer.