Arithmetic operation on a variable or reference

name += expression
name -= expression
name *= expression
name /= expression

reference += expression
reference -= expression
reference *= expression
reference /= expression

Operators perform an arithmetic operation with arguments:
   - on the left: a variable with the name or a value of the reference (element of an array or list)
   - on the right: value of the expression.
The result is written into the variable or reference used on the left side of the operator.

Example:

to vsum :a
  let "sum 0
  if array? :a || list? :a [
    foreach "x :a ["sum += :x]
  ]
  output :sum
end

to vscale :a :x
  if (array? :a || list? :a) && number? :x [
    repeat count :a [:a,repcount *= :x]
  ]
end

"v := {1 2 3 4 5}
print vsum :v
vscale :v 2
print :v

Output:

15
{2 4 6 8 10}

See also:

Variables in POOL
:= - assign new value to a variable/reference
make, name - set or create global variable
let, localmake - set or create local variable

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