I want to show you an example FLEX program that I don't understand how to analyze without the use of computer:
        int counter=0;
derp [A-Za-z]{3}[ \.]+
{derp} if (yyleng==4) return; if (counter++) yyless(1); else { REJECT;}
For the following input:
Magna turba in via est.
output is the following:
Could someone show how to debug (analyze) this code "on paper" (without the use of computer)?

Also, I have tried to follow the instructions on how to setup Visual Studio for FLEX debugging (not for error checking, but for understanding the code) on https://sourceforge.net/p/winflexbison/wiki/Visual%20Studio%20custom%20build%20rules/
, but I couldn't manage to configure it.

I have managed to work out the tutorial until "sample.l" and "sample.y" files.

After creating a "sample.l" of above code on Linux, and after running the instructions
lex -d sample.l
gcc lex.yy.c -lfl
"lex.yy.c" code is generated (I think that this should be ours "sample.y" code, is it?).

I am stuck on the next part of tutorial, where "sample.tab.h", "sample.flex.cpp" and "sample.tab.cpp" are generated. How they are generated?

Could someone please explain how to continue with this tutorial from here? Note: I don't know how to analyse FLEX programs with and without the use of computer because of this tutorial.

Does someone know another way (besides this tutorial) of configuring Visual Studio for running and debugging FLEX?