What is easier? writing many sub routines or just one long one.

i am currently writing a vba code that uses mathematical formulas to iterate and display results graphically. I am currently have an issue of reusing ending variables in next subroutine from previous subroutine. The code is mostly done except for a few debugging issues. Basically, how do I get variable from previous subroutine visible for next subroutine. Any help or direction would be greatly appreciated.