Decoding a message in C++

decode.cpp

#include <cstdio>

int decode_number(int number, int mode) 
{
	char characters[] = { '!', '?', ',', '.', ' ', ';', '"', '\'' };
	char letter;
	
	if (mode == 0) {
		number %= 27;
		letter = 'A' + number - 1;
	} else if (mode == 1) {
		number %= 27;
		letter = 'a' + number - 1;
	} else {
		number %= 9;
		letter = characters[number-1];
	} 
	
	if (number == 0) return mode = (mode + 1) % 3; 
	
	printf("%c", letter);
	
	return mode;	
}

int main() {
	FILE *fp = stdin;
	
	int ch = 0;
	int number = 0;	
	int mode = 0;
	
	while ( ((ch = getc(fp)) >= '0' && ch <= '9') || ch  == ',' )
	{	
		if ( ch != ',' )
		{
			ch = ch - '0';
			number = number * 10 + ch;
		} else {
			mode = decode_number(number, mode);
			number = 0;
		}			
	}
	
	mode = decode_number(number, mode);
	printf("\n");
	
	return 0;
}

// Test case:
// 313,12312,906,3337,2529,568,1994,689,14994,221,216,11,500,18,11684,0,136,1496,27,10
// "Poprawnie? Tak!"

decode_book.cpp

char outputCharacter;
enum modeType {UPPERCASE, LOWERCASE, PUNCTUATION}; 
modeType mode = UPPERCASE;

char digitChar; 
do {
  digitChar = cin.get();
  int number = (digitChar - '0');
  digitChar = cin.get();
  while ((digitChar != 10) && (digitChar != ',')) {
    number = number * 10 + (digitChar - '0');
    digitChar = cin.get(); 
  }

  switch (mode) { 
    case UPPERCASE:
      number = number % 27; 
      outputCharacter = number + 'A' - 1; 
      if (number == 0) {
        mode = LOWERCASE;
        continue;
      }
      break;
    case LOWERCASE:
      number = number % 27; 
      outputCharacter = number + 'a' - 1; 
      if (number == 0) {
        mode = PUNCTUATION;
        continue;
      }
      break;
    case PUNCTUATION:
      number = number % 9;
      switch (number) {
        case 1: outputCharacter = '!'; break; 
        case 2: outputCharacter = '?'; break; 
        case 3: outputCharacter = ','; break; 
        case 4: outputCharacter = '.'; break; 
        case 5: outputCharacter = ' '; break; 
        case 6: outputCharacter = ';'; break; 
        case 7: outputCharacter = '"'; break; 
        case 8: outputCharacter = '\''; break;     
      }
     if (number == 0) {
        mode = UPPERCASE;
        continue;
     }
     break; 
  }
  cout << outputCharacter; 
} while (digitChar != 10);
 
cout << "\n";