|Here I am back. Let me start by answering your questions about halt and write/writeln.|
Halt builtin function breaks the execution of the program and returns control to the operating system. The same happens at the end of the source code when the compiler gets the end. statement: a hidden halt is inseterted. Do not interpret end; as a halt directive: end marks the conclusion of a paragraph started by coding begin but does not break program execution. If not present halt, the program continues to execute after a negative side is entered.
WriteLn without parameters displays a blank line. I added that to format a nice, more readable screen; Write (without ln) displays the parameters and does not force a line feed so the next Readln accepts the value just on the same screen line.
About d:7:2 you can find a good explanation in the following on-line tutorial
select Input and Output then Formatting Output. There are a lot of Pascal tutorials on line, but many are more oriented to expert programmers than a novice. I suppose however you have a Pascal textbook.
I am happy you have all the time in the world but I guessed you are a student and the time is never enough at school. Why are you interested in Pascal, a language almost died today as ancient Greek or Latin?
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