The number of sharps in a key signature increases, as we move through what is known as ‘the cycle of 5ths'. Count up five notes from the note C, and you get to G - G major contains 1 sharp.

It does not contain any sharps or flats, hence any piece of music in C major will not have a key signature, as it is not required. On a practical level, many keyboard players like C major, as there ...