Module to assign parent part to bill of materials

I have a huge analysis I need to complete, and have a problem I think can only be solved via VB code. I have done limited VB coding in access but nothing in excel before, so hope someone could whip up something that would work and I can tinker with.

The code would have to run down the column looking for the parent part identified as 0 in column B, and then copy the parent part number in Column C to Column A for each row that has a sub part number of that parent. There can be any number of sub components but the real signal to change the parent part number would be when it hits a row with another 0 in it.

Any help here would be greatly appreciated.

0 Parent Part Number
1 Component 1 Part
1 Component 1 Part
2 Component 2 Part
0 Parent Part Number
1 Component 1 Part
1 Component 1 Part
2 Component 2 part
3 Component 3 part