Measure time interval between 4 inputs and send

Dear friends
Can anyone help to write a code for the following project.

If Gsm 800L sim module read a sms from any mobile then LDR sensor which is connected with Arduino pin A0 have to measure the time interval of 4 inputs. And send the time interval results to a mobile

Is this a class assignement?

If it is your own project, then a good place to start is by reading and following the instructions in the how to use the forum post.

You will need to describe your setup, including posting links to any modules, and a circuit diagram.

blink without delay (BWD) has the keys to the answer.

No LDR sensor is measuring anything. Please get some help writing the question. It's not understandable.
Please read the first topic telling how to use this forum, especially the information we need.