It's to easily see that memory has changed from its initial starting value, generally during debugging but sometimes for release code as well, since you can attach debuggers to the process while it's running.

It's not just memory either, many debuggers will set register contents to a sentinel value when the process starts (AIX sets its registers to 0xdeadbeef which is mildly humorous).

When and why will an OS initialise memory to 0xCD, 0xDD, etc. on malloc/free/new/delete?
Have 12 excel Sheets in a workbook for each month Jan-Dec.  Each sheet contains Names and leaves marked for that month in the same row and sum value for each category of leave at the end of the table.  I need to summarize these individual sheets value by looking for each person's Name in all sheets. how can I achieve this in excel....  I tried sum of vlookup from all sheet, it throws error or no result.  
