Excel 2007 : Need help with reference

I have a series of data in a column. For example, I have a list of 1,000 stores with three lines of information for each store. Row 2 Column C contains ai invoice reference #, e.g. 11859. This ties to store 1152. Store 1152 is referenced in Column B Row 2. Column C Rows 3 & 4 contain the invoice reference # 11859 but the store # 1152 is blank for Column B rows 3 & 4. This is the same for almost 1,000 stoes on the spreadsheet. I need to have the store referenced on every line. How can I make a formula that says "if data in Column C Row 2 is 11859 and data in Column B Row 2 is 1152, data in blank row B2 should equal data in C2 and continue that for all blank cells in Column 2? Thanks for any help.