C程序中的Char变量行为

Question

I wrote a sudoku solver program with function which checks if it is leagal to set a value in a specific location:

typedef int cell;
typedef char value;
typedef value sudokuGrid[GRID_SIZE]; // GRID_SIZE is 81


int isLegal (sudokuGrid game, cell location,value candidateDigit);

I also wrote a function to test isLegal function giving it a sudoku puzzle and once the solution is calculated checking if all set values are correct:

static void testIsLegal(){
   int i, solution;
   int mid_result, result;

   sudokuGrid testGrid = {
      '6','4','.','.','.','.','8','1','7',
      '1','7','.','8','6','.','2','.','4',
      '.','.','.','.','.','.','.','9','6',
      '.','8','.','.','9','6','.','.','.',
      '.','6','.','3','.','1','.','2','.',
      '.','.','.','2','5','.','.','6','.',
      '8','2','.','.','.','.','.','.','.',
      '3','.','7','.','1','8','.','4','2',
      '4','5','1','.','.','.','.','8','3'
   };


   printf("Testing isLegal() function ............\n");

   result = TRUE;


   solution = hasSolution(testGrid);
   showGame(testGrid);

   int f = isLegal(testGrid,78,'9');
   printf("isLegal(testGrid,78,9) = %d\n\n",f);


   i = 0;
   result = TRUE;
   value cellValue;
   if (solution){
      while ((result == TRUE) && (i < GRID_SIZE)){
         cellValue = testGrid[i];
         testGrid[i] = EMPTY_VALUE;
         printf("isLegal(testGrid,%d,%c) = %d\n",i,cellValue,isLegal(testGrid,i,cellValue));
         result = result && isLegal(testGrid,i,cellValue);
         testGrid[i] = cellValue;
         i++;
      }
    }
    if (result)
         printf("\t\t\t\t\t [OK]\n");
      else
         printf("\t\t\t\t\t[NOK]\n");
}

The result of executing this function with a wrong result is:

6 4 2   5 3 9   8 1 7
1 7 5   8 6 2   2 3 4
9 3 8   1 4 7   5 9 6

2 8 3   7 9 6   1 7 5
5 6 4   3 8 1   3 2 8
7 1 9   2 5 4   4 6 9

8 2 6   4 2 3   6 5 1
3 9 7   6 1 8   7 4 2
4 5 1   9 7 5   9 8 3

There are many mistakes here but I mentioned the both 9-s in the last line (possitions 75 and 78). Performed a manual check for isLegal(testGrid,78,'9') which returns FALSE, but when I use a loop isLegal(testGrid,i,cellValue) returns TRUE all the time:

isLegal(testGrid,78,9) = 0

isLegal(testGrid,0,6) = 1
isLegal(testGrid,1,4) = 1
isLegal(testGrid,2,2) = 1
isLegal(testGrid,3,5) = 1
.....
isLegal(testGrid,78,9) = 1
isLegal(testGrid,79,8) = 1
isLegal(testGrid,80,3) = 1

My question is why when I use char variable in ' ' quotes (isLegal(testGrid,78,'9') from the code) it shows the correct result, but not when I use cellValue variable? How can this be fixed?

Thank you!

Adding additional information:

#define MIN_VALUE '1'
#define MAX_VALUE '9'
#define EMPTY_VALUE '.'
#define NUM_VALUES (MAX_VALUE - MIN_VALUE + 1)
#define GRID_SIZE (NUM_VALUES * NUM_VALUES)
#define MAX_CELL (GRID_SIZE - 1)

#define TRUE    1
#define FALSE   0

#define MINI_SQUARE_SIZE        3
#define SQUARE_SIZE             9

typedef int cell;
typedef char value;
typedef value sudokuGrid[GRID_SIZE];

isLegal function:

int isLegal (sudokuGrid game, cell location,value candidateDigit){
   assert (location >= 0);
   assert (location <= GRID_SIZE);

   assert (candidateDigit >= MIN_VALUE);
   assert (candidateDigit <= MAX_VALUE);

   return (isLegalLine(game,location,candidateDigit) &&
            isLegalColumn(game,location,candidateDigit) &&
            isLegalSquare(game,location,candidateDigit));
}




static int isLegalLine(sudokuGrid game, cell location,value candidateDigit){
   assert (location >= 0);
   assert (location <= GRID_SIZE);

   assert (candidateDigit >= MIN_VALUE);
   assert (candidateDigit <= MAX_VALUE);


   int result, mid_result;
   int i;
   int lineNumber = location / SQUARE_SIZE;

   result = TRUE;

   for (i = 0; i < GRID_SIZE; i++){
      if (( i / SQUARE_SIZE ) == lineNumber){
         if ( game[i] != candidateDigit ){
            mid_result = TRUE;
         }
         else{
            mid_result = FALSE;
         }
         result = result && mid_result;
      }
   }

   return result;
}

static int isLegalColumn(sudokuGrid game, cell location,value candidateDigit){
   assert (location >= 0);
   assert (location <= GRID_SIZE);

   assert (candidateDigit >= MIN_VALUE);
   assert (candidateDigit <= MAX_VALUE);


   int result, mid_result;
   int i;
   int columnNumber = location % SQUARE_SIZE;

   result = TRUE;

   for (i = 0; i < GRID_SIZE; i++){
      if (( i % SQUARE_SIZE ) == columnNumber){
         if ( game[i] != candidateDigit )
             mid_result = TRUE;
         else
             mid_result = FALSE;
         result = result && mid_result;
      }
   }
   return result;
}

static int isLegalSquare(sudokuGrid game, cell location,value candidateDigit){
   assert (location >= 0);
   assert (location <= GRID_SIZE);

   assert (candidateDigit >= MIN_VALUE);
   assert (candidateDigit <= MAX_VALUE);


   int result, mid_result;
   int i;

   int lineNumber = location / SQUARE_SIZE;
   int columnNumber = location % SQUARE_SIZE;
//   int squareNumber;

   if ( lineNumber < MINI_SQUARE_SIZE){
      lineNumber = 0;
      if (columnNumber < MINI_SQUARE_SIZE){
      //   squareNumber = 1;
         columnNumber = 0;
      }
      else if (columnNumber < 2*MINI_SQUARE_SIZE){
      //   squareNumber = 2;
         columnNumber = MINI_SQUARE_SIZE;
      }
      else{
      //   squareNumber = 3;
         columnNumber = 2*MINI_SQUARE_SIZE;
      }
   }

   else if (lineNumber < 2*MINI_SQUARE_SIZE){
      lineNumber = MINI_SQUARE_SIZE;
      if (columnNumber < MINI_SQUARE_SIZE){
      //   squareNumber = 4;
         columnNumber = 0;
      }
      else if (columnNumber < 2*MINI_SQUARE_SIZE){
      //   squareNumber = 5;
         columnNumber = MINI_SQUARE_SIZE;
      }
      else{
      //   squareNumber = 6;
         columnNumber = 2*MINI_SQUARE_SIZE;
      }
   }

   else{
      lineNumber = 2*MINI_SQUARE_SIZE;
      if (columnNumber < MINI_SQUARE_SIZE){
      //   squareNumber = 7;
         columnNumber = 0;
      }
      else if (columnNumber < 2*MINI_SQUARE_SIZE){
      //   squareNumber = 8;
         columnNumber = MINI_SQUARE_SIZE;
      }
      else{
      //   squareNumber = 9;
         columnNumber = 2*MINI_SQUARE_SIZE;
      }
   }

   result = TRUE;

   int squareStartLocation = columnNumber + ( SQUARE_SIZE * lineNumber);
   int k = 0;
   int squareStartLocationLineEnd;



   while (k < MINI_SQUARE_SIZE){
      squareStartLocationLineEnd = squareStartLocation + MINI_SQUARE_SIZE;
      for (i = squareStartLocation; i < squareStartLocationLineEnd; i++){
         if (game[i] != candidateDigit)
            mid_result = TRUE;
         else
            mid_result = FALSE;
         result = result && mid_result;
      }
      k++;
      squareStartLocation += SQUARE_SIZE;
      result = result && mid_result;
  }



   return result;

}

Answer 1

Think a little bit about what this:

testGrid[i] = EMPTY_VALUE;

will do to isLegal() in the next line:

printf("isLegal(testGrid,%d,%c) = %d\n",i,cellValue,isLegal(testGrid,i,cellValue));

Maybe this does something in isLegal() what you don't want

Answer 2

Parameter candidateDigit will be passed as a char type to isLegal(). It must be the loop context causing the function to always return TRUE, so you will need to:

• show us the code for isLegal()
• show us the value of EMPTY_VALUE

Update1: Thanks for the extra info. I plugged in your filled out "bad" data, set solution to TRUE, and the test stopped at position 14 with a failure (correctly as this position contains '2' and there is another in the same line). So it seems that your code is correct! At least as far as this test goes.

Test grid:

   sudokuGrid testGrid = {
      '6','4','2','5','3','9','8','1','7',
      '1','7','5','8','6','2','2','3','4',
      '9','3','8','1','4','7','5','9','6',
      '2','8','3','7','9','6','1','7','5',
      '5','6','4','3','8','1','3','2','8',
      '7','1','9','2','5','4','4','6','9',
      '8','2','6','4','2','3','6','5','1',
      '3','9','7','6','1','8','7','4','2',
      '4','5','1','9','7','5','9','8','3'
   };

Test output:

isLegal(testGrid,78,9) = 0

isLegal(testGrid,0,6) = 1
isLegal(testGrid,1,4) = 1
isLegal(testGrid,2,2) = 1
isLegal(testGrid,3,5) = 1
isLegal(testGrid,4,3) = 1
isLegal(testGrid,5,9) = 1
isLegal(testGrid,6,8) = 1
isLegal(testGrid,7,1) = 1
isLegal(testGrid,8,7) = 1
isLegal(testGrid,9,1) = 1
isLegal(testGrid,10,7) = 1
isLegal(testGrid,11,5) = 1
isLegal(testGrid,12,8) = 1
isLegal(testGrid,13,6) = 1
isLegal(testGrid,14,2) = 0
                    [NOK]

NB Only other code changes I made were to move isLegal() below the functions that it calls (to avoid default promotion of return types) and to comment out calls to hasSolution() and showGrid().

Answer 3

If you do char a = 9 , you are making that a have an ASCII value. For example: char letter = 80; is equivalent to char letter = 'P';