Change Text To Upper, Lower Or Proper Case On Entry

I would like to format a row of cells so that when a word is entered into the cell it automatically becomes a capital.

I need the word to be capitalized so that I can use it in a custom function. The function uses the word from this cell and goes through a bunch of cases in determing how to classify the string.

I think more than one solution is possible and I would greatly appreciate some feed back, I've tried looking into turning all the letters of a string in my VBA code to capitals, or a way to format the cells, so that the string is already capitalized when entered into the VBA code, but I'm still a novice at VBA and unsure on how certain commands work.

here is a sample of my vba code.

Function WeightI(Shape As String, sDim As String, dLenFt As Double) As Double
Const pi As Double = 3.14159265358979
Const Ft2In As Double = 12
Const dDen As Double = 0.2835 ' density of steel, pounds per cubic inch

Dim aiStr() As String ' dimensions as strings