Converting words to numbers in PHP

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There are lots of pages discussing the conversion from numbers to words. Not so many for the reverse direction. The best I could find was some pseudo-code on Ask Yahoo. See http://answers.yahoo.com/question/index?qid=20090216103754AAONnDz for a nice algorithm:

Well, overall you are doing two things: Finding tokens (words that translates to numbers) and applying grammar. In short, you are building a parser for a very limited language.

The tokens you would need are:

POWER: thousand, million, billion
HUNDRED: hundred
TEN: twenty, thirty… ninety
UNIT: one, two, three, … nine,
SPECIAL: ten, eleven, twelve, … nineteen

(drop any “and”s as they are meaningless. Break hyphens into two tokens. That is sixty-five should be processed as “sixty” “five”)

Once you’ve tokenized your string, move from RIGHT TO LEFT.

  1. Grab all the tokens from the RIGHT until you hit a POWER or the whole string.

  2. Parse the tokens after the stop point for these patterns:

    SPECIAL
    TEN
    UNIT
    TEN UNIT
    UNIT HUNDRED
    UNIT HUNDRED SPECIAL
    UNIT HUNDRED TEN
    UNIT HUNDRED UNIT
    UNIT HUNDRED TEN UNIT

    (This assumes that “seventeen hundred” is not allowed in this grammar)

    This gives you the last three digits of your number.

  3. If you stopped at the whole string you are done.

  4. If you stopped at a power, start again at step 1 until you reach a higher POWER or the whole string.

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