C-在结构数组中打印2d数组的元素

Question

Im trying to make a function that sets the values of a 2D array, and then another function that prints those values.

For some reason, with my current implementation, if I create a 3x3 matrix and I set every value to the number 5, it prints the values, but it prints them counting up from 5, so it prints 567, 678, 789, when instead I want it to print the exact value that I set.

Here are the function definitions - what am I doing wrong?:

    struct matrix{
        char matrixName[50];
        int rows;
        int columns;
        float* data;
    };
    typedef struct matrix matrix_t;

int create_matrix(matrix_t* matrixP, int matrixLocation){

  char tempName[50];
  int rows, cols;


  printf("Enter a name for your matrix>\n");
  scanf("%s", tempName);

  printf("Enter the number of rows>\n");
  scanf("%d", &rows);

  printf("Enter the number of cols>\n");
  scanf("%d", &cols);

  float * our_matrix = (float *) malloc(rows * cols * sizeof(float));  

  strcpy(matrixP[matrixLocation].matrixName, tempName);
  matrixP[matrixLocation].rows = rows;
  matrixP[matrixLocation].columns = cols;
  matrixP[matrixLocation].data = our_matrix;

  return 0;

}

int setValues(matrix_t* our_matrix, int matrix_index) {
  int counter = 0;
  int row = 0, col = 0;
  for (col = 1; col <= our_matrix[matrix_index].columns; col++) {
    for (row = 1; row <= our_matrix[matrix_index].rows; row++) {
      counter++;

      printf("Enter the value for column number %d of row number %d>\n", col, row);
      scanf("%f", our_matrix[matrix_index].data+(col-1)+(row-1));                
    }
    /* separate rows by newlines */
  }
    return 0;
}

int printMatrix(matrix_t* our_matrix, int index) {
      int row = 0, col = 0;
      for (col = 1; col <= our_matrix[index].columns; col++) {
        for (row = 1; row <= our_matrix[index].rows; row++) {
      printf(" %2.f ", *our_matrix[index].data+(col-1)+(row-1));   
    }
    printf("\n");
  }
    return 0;
}

If I call the printMatrix() function without first using setValues, it seems to print the relative position of the cell that it's printing like so:

But when I call setValues() and set all values to the number 5, its prints counting up from the number 5 like this:

Answer 1

Your position calculation is incorrect. There's one problem and one 'aconventional notation' issue.

The problem is the calculation of the array subscripts:

 scanf("%f", our_matrix[matrix_index].data+(col-1)+(row-1)); printf(" %2.f ", *our_matrix[index].data+(col-1)+(row-1)); 

You need to multiply the (row - 1) value by our_matrix[matrix_index].cols . You will probably do better with some shorter names for the values:

int max_col = our_matrix[matrix_index].columns;
int max_row = our_matrix[matrix_index].rows;
float *data = our_matrix[matrix_index].data;

for (col = 1; col <= max_col; col++)
{
    for (row = 1; row <= max_row; row++)
    {
        printf("Enter the value for column number %d of row number %d>\n", col, row);
        if (scanf("%f", data + (col-1) + (row-1) * max_col) != 1)
        {
            …report error and do not continue…
        }
    }
}

for (col = 1; col <= max_col; col++)
{
    for (row = 1; row <= max_row; row++)
        printf(" %.2f", data[(col-1) + (row-1) * max_col]);
    putchar('\n');
}

That deals with the substantive bug. Note the error checking on scanf() . That is important in 'real world' programs (even if you get away without it in classes or in online contests). You could sensibly use the notation &data[(col-1) + (row-1) * max_cols] in place of data + (col-1) + (row-1) * max_cols in the call to scanf() too — that would improve the consistency of the code.

The 'aconventional notation' issue is that in C, array indexing starts at 0, not 1, and you could avoid the multitude of -1 terms by following the C conventions. This snippet also declares the loop variables when they're needed, minimizing their scope. This is a feature of C since C99 — it may not be available to you on some retrograde (but popular and widespread) platforms.

for (int col = 0; col < max_col; col++)
{
    for (int row = 0; row < max_row; row++)
        printf(" %.2f", data[col + row * max_col]);
    putchar('\n');
}