A number is a mathematical object used to count, order, or measure.

The most common system used to represent a number is the decimal system, where the base is 10 and the digits from 0 to 9 are used. The decimal system is classified as a positional notation, as it's a numerical representation where the value of each digit depends on its relative position in the whole number.

Another commonly used system is called binary, or base 2. It has 0 and 1 as digits, and is also a positional notation.

Each 0 or 1 is called a bit (short for Binary Digit). In the example to the right, the number 45 is represented by using 6 bits. Due to this feature, the binary system is widly used in computers, as it allows for logical and arithmetic operations to be performed by using only 2 digits (in other words, 2 states - yes/no, true/false, everything or nothing, on/off, 1/0) All digital electronics and computation is based in this binary system, where it's possible to represent numbers and characters, and perform logical and arithmetic operations, through the use of digital electronic circuits called logic gates. Computer programs are coded in binary, and are stored in disks in this format.

All of us are used to computers and phones. But do we truly know how these machines communicate with each other? That's right, they transfer information (like text, music and images) by using only 2 digits: 0 and 1. For each letter of the alphabet, we can associate a number. If we write that number in binary, we can write a secret message. In this game, you'll have to find the vertically written secret message. Each letter may be identified by finding out the number that's represented in the binary system in each line. Click here to play!