[c unix] nombres en lettres

char *to_string_0_9(unsigned int i){
   switch(i){
    case 0 : return "zero";
    case 1 : return "un";
    //...
    case 9 : return "neuf";
    default : break;
  }
  return "";
}

char *to_string_10_19(unsigned int){
   switch(i){
     case 10 : return "dix";
     case 11 : return "onze";
     //...
   }
   return ""
}

char *to string_20_99(unsigned int i){
   char buf[255];
   unsigned int unite,dizaine=floor(i/10);
   if (dizaine > 9 || dizaine <2 ) return "";
   int unite=i-dizaine*10;
   switch(dizaine){
      case 3 : buf="trente"
       //...
   }
   switch(unite){
     case 1 : strcat(buf,"-et-un");
     case 2 : strcat(buf,"-deux");
    //...
  }
  return &buf[0]; //enfin je crois
}

char *to_string_0_99(unsigned int){
  if (0<=i && i<9) return to_string_0_9(i);
  else if (10<=i && i<19) return to_string_10_19(i);
  else if (20<=i && i<99) return to_string_20_99(i);
  else return "";
}