I found the reason why using I,J,K variables with loop on the old FORTRAN reference.
FORTRAN has 2 types variables floating and fixed number. The type is fixed when the variable starts a letter I to N!
Programmer's reference manual Fortran (IBM704) - The Fortran Company
I found a IBM 711IBM 704 on the movie "Hidden Figures" (review@ja)
FORTRAN is the origin computer language according from the Computer History Museum. BASIC came from FORTRAN also.
Let's play with the LOOP on IchigoJam BASIC. I added a print about the the loop using FOR-NEXT command.
Please join us to make prints to learn BASIC!
"IchigoJam on GitHub"