new line within cell text

I am unsure which category to post this in, and so am cross posting this question under Excel General also.

When I want to force a new line within a cell, I can do it as I am typing by hitting alt-Enter. No problem.

However, if I want to do it programmatically, I would expect CHAR(10) to cause a line break. If not that then CHAR(13)&CHAR(10). However, no combination of these characters seems to enforce the line break; they just produce a continuous line of output with little rectangles where the unprintable characters appear.

My question: how do I enforce a new line programmatically within the text of a cell?