Function: add

Pop two elements, add them, leave result on top of stack and in varname

USAGE: add arrayname

add()
{    
  local arrayname=${1:?Array name required} varname=${2:-var}
  

Copy the array, $arrayname, to local array

  eval "array=( \"\${$arrayname[@]}\" )"
  array[1]=$(( ${array[0]} +  ${array[1]} ))
  eval "$varname=${array[1]}"
  unset array[0]
  

Copy array back to $arrayname

  eval "$arrayname=( \"\$var\" \"\${array[@]}\" )"
}