What is parameter 4 in WriteFile()

I face a problem to insert the proper lpNumberOfBytesWritten which is the parameter 4 in WriteFile(). after build, it show error "cannot convert parameter 4 from 'int *' to 'unsigned long *'. i'm sending 1 byte of data to hDevice. WriteFile(hDevice,nPtr,1,1,NULL). what's wrong with the command?
thanks.
giggs11Asked:
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nietodCommented:
The problem is that an int is signed, but it wants an unsigned value (actually a pointer to an unsigned value.)  Since the parameter is declared as LPDWORD (i.e a pointer to a DWORD) Try

DWORD BytWrt;

WriteFile(hDevice,nptr,1,&BytWrt,NULL)
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