C major

C major is a major scale based on C, which is made up of the pitches C,D,E,F,G,A,B. Its key signature has no flats or sharps.

Its relative minor is A minor, and its parallel minor is C minor. A scale in both C major and A minor can be played on a piano or other keyboard instrument using only the white keys.

Most of the time key signatures were cancelled whenever the new key signature had fewer sharps or flats than the old key signature, in modern popular music, this is only done when C major or A minor replace another key.^[1]

1. ↑ Matthew Nicholl & Richard Grudzinski, Music Notation: Preparing Scores and Parts, ed. Jonathan Feist. Boston: Berklee Press (2007): 56. ISBN 978-0-87639-074-0. "In popular and commercial music, the old key signature is cancelled only if the new key is C major or A minor."