at the first i am sorry for writing in english and this is because my keyboard is english, anyway
I do not know the circuit but as far as i know the PIC cannot stand voltage more than 5 voltge.
I gues that there is a voltage divider circuit infront of the input pin Porta.3
for build such a project we should specify the range of voltage such as 24 volt.
then we should specify the voltage divider at the input of the analog to digital pin ( we should keep in our mind thet the voltage should not be more than 5 volt) in our case if the max voltage is 24 volt then we should use R1=2.5k and R2=10k ( the max voltge will be 4.8 if the input volt is 24 volt)
after that we should know how many bits in my digital to anlog converter assume that we have 10 bits then we have 1024 steps each step will represent the value of Vmax/ 1024 which is 24/1024
in our case the resolution is 0.0234375 volt
then after that u write the program
as the following
1- read the ADC in x ( x as float)
2-Temp = x *0.0234375
3- display the result in 3 digit (7 segment )
if i have time i will write the program in PICBASIC with the simulation in PROTEUS
in shaa allah