This is a somewhat debated question all around the world! Is a Piano a string instrument?
Yes and No
The Piano does actually have strings. Inside there are strings attributed to every single key on the piano.
When you hit a key with your finger, it causes a felt-covered hammer inside the Piano to strike one of the strings. This produces the sound.
But, because the sound is produced by striking the string rather than using a plucking method or a bow, it is also often classed as a Percussion Instrument.
The Piano has a total of 88 keys, therefore has 88 strings and hammers that strike them!
Each string is a differing length dependant on the position on the piano. The deeper the note, the longer the string.
This also corresponds to the size and shape of a Piano.