Or you can select all the cells you want filled (say E1:E20), then type in the formula in the formula bar (= D1-C1). Then instead of ENTER, use CTRL + SHIFT + ENTER. All cells will be filled with the appropriate formula.
old, slow, and confused
but at least I'm inconsistent!
That kind of worked. The only problem is that now I have the EXACT same formula in each cell in column E. Each cell in E is now "C1-D1". I need it to be specific for each row it's in. For example, E1 should be C1-D1, E2 should be C2-D2, E3 should be C3-D3, etc... Is there a way to do that?