Setting values of a dynamically allocated array - c

Question

I am trying to create and store values inside a matrix, represented as a 1 dimensional array.
When I try to set the values, my output comes out wrong.
Matrix Struct
struct matrix{
char matrixName[50];
int rows;
int columns;
float* data;
};
typedef struct matrix matrix_t;
matrix_t our_matrix[MAX_MATRICES];
Creating the matrix:
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 * data = (float *) malloc(rows * cols * sizeof(float));
int row = 0, col = 0;
for (row = 1; row <= rows; row++) {
for (col = 1; col <= cols; col++) {
data[(row-1) + (col-1) * cols] = 0;
}
}
strcpy(matrixP[matrixLocation].matrixName, tempName);
matrixP[matrixLocation].rows = rows;
matrixP[matrixLocation].columns = cols;
matrixP[matrixLocation].data = data;
return 0;
}
Setting Values:
int setValues(matrix_t* our_matrix, int number_of_matrices) {
int i, matrix_index;
for(i = 0; i < number_of_matrices; i++){
printf("Matrix %i\t %i Rows\t %i Columns - Name: %s\n", i+1, our_matrix[i].rows, our_matrix[i].columns, our_matrix[i].matrixName);
}
printf("\nWhich matrix would you like to set the values for?\n");
printf("Select a matrix number from the list above>\n");
scanf("%d", &matrix_index);
while(matrix_index < 1 || matrix_index > number_of_matrices){
printf("Enter a number from the list of available matrices - number must be greater than zero and less than or equal to the number of available matrices:\n");
scanf("%d", &matrix_index);
}
int max;
matrix_index -= 1;
max = our_matrix[matrix_index].columns;
float *data = our_matrix[matrix_index].data;
int row = 0, col = 0;
for (row = 0; row < our_matrix[matrix_index].rows; row++) {
for (col = 0; col < our_matrix[matrix_index].columns; col++) {
printf("Enter the value for column number %d of row number %d>\n", col+1, row+2);
scanf("%f", &data[(row) + (col) * (max)]);
}
/* separate rows by newlines */
}
our_matrix[matrix_index].data = data;
return 0;
}
When I try call setValues on a 5 x 2 matrix and I give it the values 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 these are the values that I get:
I honestly can't fathom how it stores those values and not the 1:10 that i'm passing it.

Answer 1

You have one little confusion in address computation: You inverted row ans col in multiplication.
You write (I replaced max by its value) in setValues
scanf("%f", &data[(row) + (col) * (our_matrix[matrix_index].columns)]);
the same in create_matrix function:
data[(row-1) + (col-1) * cols] = 0;
You should have written:
scanf("%f", &data[(col) + (row) * (our_matrix[matrix_index].columns)]);
and
data[(col-1) + (row-1) * cols] = 0;
You can do the math to be convinced:
If rows is 2 and cols is 10, with your method, the max index is 2 + 9 * 10 = 90, it's too big for a 2x10 matrix.
One more thing:
The function create_matrix can be simplified:
int create_matrix(matrix_t* matrixP, int matrixLocation){
int rows, cols;
printf("Enter a name for your matrix>\n");
/* Warning, you should test what scanf returned! */
scanf("%s", matrixP[matrixLocation].matrixName);
printf("Enter the number of rows>\n");
/* Warning, you should test what scanf returned! */
scanf("%d", &rows);
printf("Enter the number of cols>\n");
/* Warning, you should test what scanf returned! */
scanf("%d", &cols);
matrixP[matrixLocation].rows = rows;
matrixP[matrixLocation].cols = cols;
/* Warning, you should test what calloc returned! */
matrixP[matrixLocation].data = calloc(rows * cols, sizeof(float));
return 0;
}