Question

I’m puzzled as to how the header, return and call would look.

This is what gave me the error “Wrong pointer type”

        int **CreatesArray (int r,int c)
    {
        int table [r][c];
        printf ("Enter clause orientations.\n");
        for (int i = 0; i<r;i++)
            {
                for (int j = 0;j<c;j++)
                    {
                        scanf ("%d",&table[i][j]);
                    }
            }
        return table;
    }

Function call from main:

int **tableaux;

tableaux = CreatesArray(ROWS,COLS);

Why is this not the correct way of doing it?

NOTE: Will post TableCreator shortly

Answer 1

Your function is a little off. For one thing, you’re creating the two-dimensional array table[r][c] on the stack, and you can’t return stack-allocated arrays from functions in C.

You will have to allocate the table on the heap, and return that. Here’s an example:

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

int** create_table (int r,int c)
{
    // malloc the row pointers
    // in case you're wondering what I'm doing with sizeof(*table),
    // it's getting the size of *table which is the size of the 
    // underlying pointer type, because we will be allocating the 
    // column pointers. C allows this seemingly weird syntax 
    // because sizeof does not evaluate its operand.

    int **table = malloc(r * sizeof(*table));

    // for each row pointer, allocate 'c' column pointers
    for (int i = 0; i < r; ++i) {
        // sizeof(**table) gets the underlying type of a double-dereference,
        // which is sizeof(int) in this case.
        table[i] = malloc(c * sizeof(**table));
    }

    // read into your table
    for (int row = 0; row < r; ++row) {
        for (int col = 0; col < c; ++col) {
            printf("Enter orientation for table[%d][%d]: ", row, col);
            scanf ("%d",&table[0][0]);
        }
    }

    return table;
}

int main() {
    int row = 10;
    int col = 10;
    int **table = create_table(row, col);

    for (int r = 0; r < row; ++r) {
        for (int c = 0; c < col; ++c) {
            printf("table[%d][%d]: %d\n", r, c, table[r][c]);
        }
    }

    // free all the column pointers
    for (int i = 0; i < row; ++i) {
        free(table[i]);
    }

    // free the row pointers
    free(table);

    return 0;
}

If you don’t know about C memory allocation and management, read some stuff here:

• Dynamically allocating multidimensional arrays in C
• C Memory Allocation