这两条线

// Convert to uppercase
int toupper(int word1);
int toupper(int word2);

只不过是同一个函数toupper的声明。
如果你想把字符串转换成大写，你可以自己编写一个单独的函数，例如

string string_toupper( string word )
{
    for ( string s = word; *s != '\0'; ++s )
    {
        *s = toupper( ( unsigned char ) *s );
    }

    return word;
}

在main中，而不是上面所示的两行

// Convert to uppercase
string_toupper( word1 );
string_toupper( word2 );

函数compute_score中的for循环

for (i=0; i<n1 + n2; i++) {

由于访问索引在[0, n1 + n2)范围内的字符串之外的内存，导致未定义的行为
相反，编写一个单独的函数来计算字符串的得分，如

int compute_score( string word )
{
    int score = 0;

    string letters = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
    // Points assigned to each letter of the alphabet
    int POINTS[] = {1, 3, 3, 2, 1, 4, 2, 4, 1, 8, 5, 1, 3, 1, 1, 3, 10, 1, 1, 1, 1, 4, 4, 8, 4, 10};

    for ( ; *word != '\0'; ++word ) 
    {
        string p = strchr( letters, *word );
        if ( p != NULL ) score += POINTS[p - letters];
    }

    return score;
}

在main中你可以写

int score1 = compute_score( word1 );
int score2 = compute_score( word2 );

// TODO: Print the winner
if ( score2 < score1 ) {
    puts("Player 1 Wins!");
}
else if ( score1 < score2 ) {
    puts("Player 2 Wins!");
}
else {
    puts("Tie!");
}

请注意，使用char *和const char *来代替typedef名称string会更好。

下面的解决方案是使用Ada编程语言完成的。这是为了表明，选择解决问题的语言可以影响解决方案的表达方式。

-- Ada version of CS50 Lab 2

with Ada.Text_IO;             use Ada.Text_IO;
with Ada.Characters.Handling; use Ada.Characters.Handling;

procedure Main is
   subtype Upper_Case is Character range 'A' .. 'Z';
   Letters : constant array (Upper_Case) of Positive :=
     ('A' => 1, 'B' => 3, 'C' => 3, 'D' => 2, 'E' => 1, 'F' => 4, 'G' => 2,
      'H' => 4, 'I' => 1, 'J' => 8, 'K' => 5, 'L' => 1, 'M' => 3, 'N' => 1,
      'O' => 1, 'P' => 3, 'Q' => 10, 'R' => 1, 'S' => 1, 'T' => 1, 'U' => 1,
      'V' => 4, 'W' => 4, 'X' => 8, 'Y' => 4, 'Z' => 10);
   type Winner is (Player1, Player2, tie);

   function compute_score (left : String; right : String) return Winner is
      p1   : Natural := 0;
      p2   : Natural := 0;
      Temp : Character;
   begin
      for value of left loop
         Temp := To_Upper (value);
         if Temp in Upper_Case then
            p1 := p1 + Letters (Temp);
         end if;
      end loop;
      for value of right loop
         Temp := To_Upper (value);
         if Temp in Upper_Case then
            p2 := p2 + Letters (Temp);
         end if;
      end loop;
      if p1 > p2 then
         return Player1;
      elsif p2 > p1 then
         return Player2;
      else
         return tie;
      end if;
   end compute_score;

begin
   Put ("Enter two lines of text:");
   declare
      Line1  : String := Get_Line;
      Line2  : String := Get_Line;
      Result : Winner;
   begin
      Result := compute_score (Line1, Line2);
      case Result is
         when Player1 =>
            Put_Line ("Player 1 wins");
         when Player2 =>
            Put_Line ("Player 2 wins");
         when tie =>
            Put_Line ("Tie");
      end case;
   end;
end Main;

分数仅基于字母，而不是输入字符串中的任何其他字符。您必须确保您没有试图累积白色、数字或标点符号的分数。