Problem in inserting in an array

Question

I have a csv files having nos from 1-100 which are not consequitive and have some respective values along with it. I wanted to modify the file by making it consequetive  by adding the missing values and putting NULL against the newly added values and save the modification to another file.

For this I want to take two arrays in one I am taking the first column of the csv file and in the other I am taking the last no as the limit and incrementing it.
After that I am trying tp compare it and while comparing wanted to replace the missing values.

Please help me in this regard.