What are the sign conventions of heat, work and internal energy?

The sign conventions are as follows:
i) When heat is supplied to a system, dQ is positive. When heat is drawn from the system, dQ is negative. 
ii) When the gas expands, work is done by the gas (dW is positive). When gas is compressed, work is done on the gas (dW is negative). 
iii) When the temperature of gas increases, it's internal energy increases, dU is taken as positive. When the temperature of gas decreases, internal energy decreases and dU is taken as negative.