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 (see below: Scales and keys).
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.