download and install dependencies
-- https://sourceforge.net/projects/gnuwin32/files/bison/
-- https://sourceforge.net/projects/gnuwin32/files/flex/
-- C compiler
-- https://www.youtube.com/watch?v=0MUULWzswQE
compile and run
flex scanner.l // gives ==> lex.yy.c
gcc lex.yy.c // gives ==> a.exe
./a.exe // give input