I need to make a table that evaluates a number.

If a number (x) is between (A) and (B), then I have to do a calculation (C1)
If a number is between (B) and (C), then I have to do a calculation (C2)
If a number is between C and D, then I have to do a calculation (C3)
If a number is greater than D, then I have to do calculation (C4)

I just can't seem to get the calculations to come out correct.