A number is a mathematical object used to count, measure and label. Questions about using numbers in variables processing, numbers processing, conversion, display, logical numerical changes, data type existence, etc. For questions regarding phone numbers, please use tag [phone-number].
Different types of numbers are used in many cases. Numbers can be classified into sets, called number systems.
Natural numbers
The most familiar numbers are the natural numbers or counting numbers (1, 2, 3, ...). Zero is usually not considered a natural number, although definitions vary.
Integers
The integers are formed by the natural numbers (including 0) (0, 1, 2, 3, ...) together with the negatives of the non-zero natural numbers (−1, −2, −3, ...). Viewed as a subset of the real numbers, they are numbers that can be written without a fractional or decimal component, and fall within the set {..., −2, −1, 0, 1, 2, ...}.
Rational numbers
A rational number is a number that can be expressed as a fraction with an integer numerator and a non-zero natural number denominator. Fractions are written as two numbers, the numerator and the denominator, with a dividing bar between them.
A number is rational if (and only if) it can be written as a terminating and/or repeating decimal.
Real numbers
The real numbers include all of the measuring numbers. Real numbers are usually written using decimal numerals, in which a decimal point is placed to the right of the digit with place value one. Each digit to the right of the decimal point has a place value one-tenth of the place value of the digit to its left.
Complex numbers
The complex numbers consist of all numbers of the form
a + b*i
where a and b are real numbers and i is the square root of negative one (the imaginary unit).
