music(sharp and flat)

First of all you have to look at the key signature(調號).
If there is no sharps or flats after the treble(高音譜號)or bass clef(低音譜號 )clefs, there's no need to sharp or flat any notes in that piece of music. The key is in C major or A minor.
If there's an F# after the key signature, it means that all the notes F has raised one semitone in pitch. You have to play the F# rather than the F note in that piece of music.
如果是G major 要 sharp F note.
如果是A major 又要 sharp F,C,G note.
即是說:1個sharp在琴譜的前面（即：調號中含有1個#）是G major or E minor，而 G major要升 F 音，即係在鋼琴上逢是F音都要彈黑鍵。

3個sharp在琴譜的前面（即：調號中含有3個#）是A major or F# minor。
逢是寫在琴譜前面——任何譜號(clef)之後而寫既sharp and flat都稱為調號(key signature)。

#係flat
b係sharp
G major 同睇番有冇b/#