Line Drawing Fonts

I'm attempting to program a C style comment generator and wanted to add a closed rectangle.  I thought there were extended characters with some fonts that I could use, but haven't been able to find any except the underscore (I don't want gaps in the lines.) So I would need a "topscore" -- like the underscore except at the top, and vertical lines far left and right.  Even better would be corner lines like left/upper, right/upper, left/lower, and right/lower.