Q:

Shell # inside (( ))

I am new to shell.  I am not quite understand the following function.  This function basically increase the hour by 1.  
I am wondering why the developer put "10#" in front of $g_current_hour+1.  From my understanding, dose # in shell means comments? 
f_increment_hour() {
    g_next_hour=$((10#$g_current_hour+1))
}

A:

Everything depends on the context.  Here 10# means base 10. 

Constants with a leading 0 are interpreted as octal numbers.   A
  leading 0x or 0X denotes hexadecimal.   Otherwise, numbers take  the 
  form  [base#]n,  where  the optional base is a decimal number between
  2 and 64 representing the arithmetic base, and n is a number in that
  base.   If base# is omitted, then base 10 is used.