I create new topic because, I have not received a reply.
I have to hand over homework, but I do not know how to do it.So I wrote here, that's the problem itself:
The task of the day: Create a program that opens the file, displays its contents, add each number from the file. (to date to evaluate 3) displayed at a given character in the file (which will ask which character I want to see) (4) will add text to a file and save it.