Real numbers include rational numbers (numbers which can be represented as a fraction of two integers) and irrational numbers (numbers that can't be represented as a fraction - the most famous one is probably π). Since irrational numbers have an infinite number of decimal places, they obviously can't be stored as a floating point value and also can't be written down exactly, no matter how many decimal places you use. "Arbitrary precision" constants might get you closer, but yes, you will never be able to store a "true" irrational number in a computer.