Macro for Filling the empty cells based on current date.

Dear Friends,

I have a spreadsheet for entering Employee's details. On that I am entering employees daily attendance status. It is almost 600 employees and entering each every employee is a herculean task. So What I think was I can enter on the Absent, and Casual Leave, etc and remaining staff will be PRESENT. So that If I get a command button for that, I need to apply "P" on the remaining cells on that particular column. More clearly, I have 31 columns on day basis and on each column's 7th ROW contains that particular days date. So the macro has to search the empty CELL's between that date's particular column and fill it with "P". The Status rows will be between 8:500 on each day. One more thing the macro has to check. The empty cell on each day has to fill only if that cells respective "B" cell having any value. More clear I am entering Employees name in the "B" Column from 8:500. So, After clicking the command button, macro has to find that particular date containing column and find the empty cells between that column 8th ROW to 500th ROW and has to fill that CELL with "P" ONLY IF there is any name in the B column.

Kindly Suggest me a macro for this.