This question already has an answer here:
as an example, I have the wallet with address-A (with 10 BTC)
If I send 1 BTC to someone (address-B) then in transaction I see
address-A > 1 BTC > address-B
address-A > 1 BTC > address-C
after, on address-A I have 8 BTC, but my bitcoin-qt show me 9 BTC (as it must be)
why it makes sends to strange address-C ?
Found an answer here https://en.bitcoin.it/wiki/Change