Name that Number

program NameThatNumber;

uses sysutils;

const
  letterDict: array [0..9] of string = ('', '', 'ABC', 'DEF', 'GHI', 'JKL', 'MNO', 'PQRS', 'TUV', 'WXYZ');

function getNumberFromLetter(letter: char): integer;
var
  number, letterDictCount: integer;
begin
  number := -1;
  for letterDictCount := 0 to 9 do
    if pos(letter, letterDict[letterDictCount]) <> 0 then
      number := letterDictCount;
  getNumberFromLetter := number;
end;

procedure main();
var
  userInput, number: string;
  userInputCount, tempNumber: integer;
  failed: boolean;
begin
  write('Enter a string of letters: ');
  readln(userInput);
  failed := false;
  for userInputCount := 1 to length(userInput) do
    if userInput[userInputCount] = ' ' then
      number := concat(number, ' ')
    else
      begin
        tempNumber := getNumberFromLetter(upcase(userInput)[userInputCount]);
        if tempNumber = -1 then
          begin
            failed := true;
            break;
          end
        else
          number := concat(number, inttostr(tempNumber));
      end;
  if failed then
    writeln('Invalid input!')
  else
    writeln(number);
end;

begin
  main();
  readln;
end.