strings.forth

: print ( ptr len -- )
  0 do
    dup
    i + C@
    dup 0= if
      drop
      leave
    then
    emit
  loop
  drop
  ;

: readln ( ptr len -- )
  0 do
    key
    dup 10 = if
      drop
      0 over C!
      leave
    then
    over
    C!
    1 +
  loop
  drop
  ;

: itoa ( value base ptr len -- )
  0 do
    >R
    dup >R
    over over /
    >R
    mod
    R> swap
    R> swap
    48 +
    R> dup 1 + >R
    C!

    over 0= if
      R>
      dup
      0 swap C!
      leave
    then
    R>
  loop
  drop
  drop
  drop
  ;

: strlen ( ptr len -- len )
  over swap
  0 do
    dup
    C@
    0= if
      leave
    then
    1 +
  loop
  swap
  -
  ;

: cmemswap ( a b -- )
  dup C@ >R
  over C@ >R
  \  a b      bval aval
  R> swap C!
  R> swap C!
  ;

: strrev ( ptr len -- )
  dup >R
  over swap strlen
  1 -
  over +
  R> 0 do   \ ptr endptr
    over over = if
      leave
    then
    over over > if
      leave
    then

    over over cmemswap

    swap 1 + swap
    1 -
  loop
  drop drop
  ;

create test 10 0 do 0 c, loop
12345 10 test 10 itoa
test 10 strrev
test 10 print