C not printing 2D dynamic array content

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I am trying to make a 2D dynamic array that calculates the derteminant of 4 or 9 numbers.

While using pointers and a dynamic array worked flawlessly in a 1D array, I can't wrap my head around what I have to do to make it owrk in 2D. So far, the program compiles properly and receives input. However, it does not print anything. I even tried printing a single cell content. Nothing.

Here is the code:

  #include <stdio.h>
    #include <stdlib.h>
    
    int size; int i; int j; int **arDet; int a; int b; int c; int d; int e; int f; int g; int h;
    
    int input()
    {
        do
        {
            scanf("%d", &size);
        }while(size > 3 || size < 2);
        arDet = (int**)malloc(sizeof(int)*size);
        for(i = 0 ; i < size; i++)
        {
            for(j = 0 ; j < size; j++)
            {
                scanf("%d", &arDet[i][j]);
            }
        }
    }
    
    int main()
    {
        input();
        if(size == 2)
        {
            printf("%d\n", arDet[0][0]*arDet[1][1] - arDet[0][1]*arDet[1][0]); 
            return 0;
        }else if(size == 3)
        {
           // printf("%d", arDet[0]*(arDet[4]*arDet[8] - arDet[7]*arDet[5]) - arDet[1]*(arDet[3]*arDet[8] - arDet[5]*arDet[6]) + arDet[2]*(arDet[3]*arDet[7] - arDet[6]*arDet[4]));
            return 0;
        }else
        {
            return -1;
        }
    }
dynamic-arrays printing c arrays
1 Answers
  • You only allocated an array to store pointers to each rows. You have to allocate arrays to store values for each rows.
  • The size calculation for arDet is wrong. The elements of arDet are int*. int (4 bytes for example) has shorter size than int* (8 bytes for example) in some environments and your code will cause trouble in such environments.
  • Casting results of malloc() in C is discouraged.
    arDet = malloc(sizeof(arDet[0])*size); /* fix size calculation */
    for(i = 0 ; i < size; i++)
    {
        arDet[i] = malloc(sizeof(arDet[i][0]) * size); /* add this */
        for(j = 0 ; j < size; j++)
        {
            scanf("%d", &arDet[i][j]);
        }
    }

Also note that the commented line

       // printf("%d", arDet[0]*(arDet[4]*arDet[8] - arDet[7]*arDet[5]) - arDet[1]*(arDet[3]*arDet[8] - arDet[5]*arDet[6]) + arDet[2]*(arDet[3]*arDet[7] - arDet[6]*arDet[4]));

doesn't make sense because C doesn't support multiplying two pointers and indice above 2 is out-of-range when size is 3.

user_40623540
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