HP71B/75: How to use SUB, ENDSUB, CALL

[Garth Wilson]

A nice thing about SUBprograms is that they have local environments, so they don't step on identically named variables, etc. from other programs or subprograms that might be pending. A subprogram can even call itself recursively, up to 63 levels deep IIRC, and each level will have its own environment. The subprogram does not have to be in the same program file; and if there might be two or more subprograms with the same name, you can specify where to look to find the right one. The CALL can also be indirect, with the subprogram's name being in a string. It's really quite powerful. The list in input and output parameters can be quite long. This is all 71 stuff. I don't know if the 75 differs.