How can i cover an ASCII file and use the data i want(certain blocks) rather than storing in structures or matrix?

Hello. I want to cover an ASCII file , and use a part of it , 1 block or more. How can i just cover and not save the data i want to use in calculations ,in arrays or sturctures.

I want to use the data from block (under header) for 2 types of calculations. First i want to use the data from the nn line,then the data from the line with the index i choose,for example,after the nn line , there are h -lines, and i want h7 line , not h1 or other. Because i have a very large number of blocks in my ASCII file , it takes more than 15 seconds to finish the calculations , because it saves the data i want in structures. I need just to scan them , to identify the ones i need , with the indexes i need , and use them rather than saving . I hope my questions it's understandable and i apologize for my bad English. Also i want to say that i am very noob at this program and i need the explanation very detailed. Thank you! P.S. Look on the attachament for the example of ASCII file.