Error:expected declaration before { token. (Havent i already declared it?)
Probably the error is in line

dht.begin();


You did not declare the variable dht, probably of type DHT11 ? You can find the correct class name in the dht.h header file.

After checking this (random) website compute heat index arduino about DHT11 I see the line:

DHT dht(DHTPIN, DHTTYPE);


Which you also have to add, probably as:

DHT dht(DHT11_PIN, DHTTYPE);