comparision of 2 old temperature reading with 2 new temperature reading in Arduino

I'm working on a project which has 2 LM35 sensors. I need to use interrupts in my Arduino to compare the temperatures read every 3 seconds. Every 3 seconds 2 sensors will be read and the new temperatures must be compared with the temperatures recorded 3 seconds earlier .

if the new temperature are equal to the old ones, then it should be print the value and switch to next state. How should I define the variable and code this. please help. I'm new to programming.

if my question is not clear, please do not mind to ask.