THERMOSTATE PROJECT HELP NEED

Dear expert sir,

I want to make a project of temperature controlled system .Thermostat. Here i use PIC16f877a MCU , DHT22 , 1602 LCD, and 4 push switch (MODE,  ++,  –,  ok ) but here is the problem . I am not know how to write code for Push switch function. Actually I want  set the value of    Min and Max temperature by push on button  . In my code the variable name is {  T_min, T_max }, and the value is always save on EEPROM. If any one help my ,I am proud of him.

Here i attach my file.

semilution file, source code, hex file

https://drive.google.com/open?id=0B_sqaR1tOdGvczl3RWJ1Q2N1OXM