Converting numbers to text, C++

Question

For an input number say 232, I wanted to be able to write out the number in text form: two hundred thirty two. I have an array which holds these numbers

Array[0] = 2, Array[1] = 3, Array[2] = 2.

I have written a

switch statement

which sees the number and prints it text, example two hundred three two. I don't know how transform that "three" into "thirty" dynamically. Suppose I have more numbers to spell, like 452,232.

Answer 1

You can't handle digits independently, it's that simple.

For example, the text for 21 is the concatenation of "twenty" and "one", but the text for 11 is not the concatenation of "ten" and "one".

Also, "1001" doesn't become "one thousand zero hundred zero one".

You can use function calls to keep logic complexity down, but you're going to need logic to look at multiple digits at once.

Answer 2

Check out this implementation over at wikipedia. It is probably what you want

Copied directly from wikipedia, should the link become broken.
Do see the link first, if an improved solution would be written

#include <string>
#include <iostream>
using std::string;

const char* smallNumbers[] = {
  "zero", "one", "two", "three", "four", "five",
  "six", "seven", "eight", "nine", "ten",
  "eleven", "twelve", "thirteen", "fourteen", "fifteen",
  "sixteen", "seventeen", "eighteen", "nineteen"
};

string spellHundreds(unsigned n) {
  string res;
  if (n > 99) {
    res = smallNumbers[n/100];
    res += " hundred";
    n %= 100;
    if (n) res += " and ";
  }
  if (n >= 20) {
    static const char* Decades[] = {
      "", "", "twenty", "thirty", "forty",
      "fifty", "sixty", "seventy", "eighty", "ninety"
    };
    res += Decades[n/10];
    n %= 10;
    if (n) res += "-";
  }
  if (n < 20 && n > 0)
    res += smallNumbers[n];
  return res;
}


const char* thousandPowers[] = {
  " billion", " million",  " thousand", "" };

typedef unsigned long Spellable;

string spell(Spellable n) {
  if (n < 20) return smallNumbers[n];
  string res;
  const char** pScaleName = thousandPowers;
  Spellable scaleFactor = 1000000000;   // 1 billion
  while (scaleFactor > 0) {
    if (n >= scaleFactor) {
      Spellable h = n / scaleFactor;
      res += spellHundreds(h) + *pScaleName;
      n %= scaleFactor;
      if (n) res += ", ";
    }
    scaleFactor /= 1000;
    ++pScaleName;
  }
  return res;
}

int main() {
#define SPELL_IT(x) std::cout << #x " " << spell(x) << std::endl;
  SPELL_IT(      99);
  SPELL_IT(     300);
  SPELL_IT(     310);
  SPELL_IT(    1501);
  SPELL_IT(   12609);
  SPELL_IT(  512609);
  SPELL_IT(43112609);
  SPELL_IT(1234567890);
  return 0;
}