The problem:

I have a (big) column of numbers, most of which are 3-digit, some of them are 2-digit. I'd like to replace every two-digit number with first 3-digit number above.

My question:

Is there a way to do that? I was thinking of assigning a function to each cell in a column. This function would replace the value with a previous 3-digit if the value in cell was 2-digit, BUT do not change the value in the cell if it was 3-digit. But how do I insert a function into a full cell?