Hexadecimal numbers

The hexadecimal system has base 16, so it needs sixteen symbols. The first ten are the digits 0 to 9. The other six are the letters A, B, C, D, E and F, with the values A = 10, B = 11, C = 12, D = 13, E = 14 and F = 15. In a hexadecimal number these letters are digits, not parts of a word: in 3E9 the E is a digit worth 14. In this course we write the letters as capitals. The ready functions of PHP and VB.NET print them in lower case (3e9), which is exactly the same number. After F comes 10, which in hexadecimal means one sixteen and no ones. Why use it? It writes long binary numbers short, because one hexadecimal symbol stands for exactly four bits (you will see this next week). So memory addresses, colour codes in some programming languages and the hardware address of a network card are often written in hexadecimal. It is only a way of writing a number: the data stay the same.