Parsing .csv file into 2D array in C

It looks like commenters have already helped you find a few errors in your code. However, the problems are pretty entrenched. One of the biggest issues is that you're using strings. Strings are, of course, char arrays; that means that there's already a dimension in use.

It would probably be better to just use a struct like this:

struct csvTable
{
    char sku[10];
    char plant[10];
    char qty[10];
};

That will also allow you to set your columns to the right data types (it looks like SKU could be an int, but I don't know the context).

Here's an example of that implementation. I apologize for the mess, it's adapted on the fly from something I was already working on.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

// Based on your estimate
// You could make this adaptive or dynamic

#define rowNum 500000

struct csvTable
{
    char sku[10];
    char plant[10];
    char qty[10];
};

// Declare table
struct csvTable table[rowNum];

int main()
{
    // Load file
    FILE* fp = fopen("demo.csv", "r");

    if (fp == NULL)
    {
        printf("Couldn't open file\n");
        return 0;
    }

    for (int counter = 0; counter < rowNum; counter++)
    {
        char entry[100];
        fgets(entry, 100, fp);

        char *sku = strtok(entry, ",");
        char *plant = strtok(NULL, ",");
        char *qty = strtok(NULL, ",");

        if (sku != NULL && plant != NULL && qty != NULL)
        {
            strcpy(table[counter].sku, sku);
            strcpy(table[counter].plant, plant);
            strcpy(table[counter].qty, qty);
        }
        else
        {
            strcpy(table[counter].sku, "\0");
            strcpy(table[counter].plant, "\0");
            strcpy(table[counter].qty, "\0");
        }
    }

    // Prove that the process worked
    for (int printCounter = 0; printCounter < rowNum; printCounter++)
    {
        printf("Row %d: column 1 = %s, column 2 = %s, column 3 = %s\n", 
            printCounter + 1, table[printCounter].sku, 
            table[printCounter].plant, table[printCounter].qty);
    }

    // Wait for keypress to exit
    getchar();

}

There are multiple problems in your code:

• In the second loop, you do not stop reading the file after 10 lines, so you would try and store elements beyond the end of the A array.
• You do not reset j to 0 at the start of the while (j < 10) loop. j happens to have the value 10 at the end of the initialization loop, so you effectively do not store anything into the matrix.
• The matrix A should be a 2D array of char *, not int, or potentially an array of structures.

Here is a simpler version with an allocated array of structures:

#include <stdio.h>
#include <stdlib.h>

typedef struct item_t {
    char SKU[20];
    char Plant[20];
    char Qty[20];
};

int main(void) {
    FILE *stream = fopen("input/input.csv", "r");
    char line[200];
    int size = 0, len = 0, i, c;
    item_t *A = NULL;

    if (stream) {
        while (fgets(line, sizeof(line), stream)) {
            if (len == size) {
                size = size ? size * 2 : 1000;
                A = realloc(A, sizeof(*A) * size);
                if (A == NULL) {
                    fprintf(stderr, "out of memory for %d items\n", size);
                    return 1;
                }
            }
            if (sscanf(line, "%19[^,\n],%19[^,\n],%19[^,\n]%c",
                       A[len].SKU, A[len].Plant, A[len].Qty, &c) != 4
            ||  c != '\n') {
                fprintf(stderr, "invalid format: %s\n, line);
            } else {
                len++;
            }
        }
        fclose(stream);

        //print matrix
        for (i = 0; i < len; i++) {
            printf("%s,%s,%s\n", A[i].SKU, A[i].Plant, A[i].Qty);
        }
        free(A);
    }
    return 0;
}