/*
 * Program to demonstrate 2D array using malloc, two ways.
 */
#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>

void printarray(int rows, int cols, int **nums) {
	for (int r = 0; r < rows; ++r) {
		for (int c = 0; c < cols; ++c) {
			printf("%10d ", nums[r][c]);
		}
		putchar('\n');
	}
}
void fill(int rows, int cols, int **nums) {
	for (int r = 0; r < rows; ++r) {
		for (int c = 0; c < cols; ++c) {
			nums[r][c] = 1000 * r + c;
		}
	}
}

int main(void) {

	printf("enter rows, cols\n");
	int rows, cols;
	if (scanf("%d %d", &rows, &cols) != 2) {
		printf("error\n");
		return 1;
	}

	/* 
	 * one way to make a 2D array:
	 * allocate each row separately
	 */

	/* array of pointers to rows */
	int **row_ptrs1 = malloc(sizeof(row_ptrs1[0]) * rows);

	/* fill array of pointers to rows */
	for (int r = 0; r < rows; ++r) {
		row_ptrs1[r] = malloc(sizeof(row_ptrs1[0][0]) * cols);
	}

	/* fill and print array */
	fill(rows, cols, row_ptrs1);
	printarray(rows, cols, row_ptrs1);

	/* free allocated space */
	for (int r = 0; r < rows; ++r) {
		free(row_ptrs1[r]);
	}
	free(row_ptrs1);

	/* 
	 * another way to make a 2D array:
	 * allocate one big block of space, and build pointers into it
	 */

	/* array of pointers to rows */
	int **row_ptrs2 = malloc(sizeof(row_ptrs2[0]) * rows);

	/* space for all rows */
	int *nums = malloc(sizeof(nums[0]) * rows * cols);

	/* fill array of pointers to rows */
	for (int r = 0; r < rows; ++r) {
		row_ptrs2[r] = &nums[r*cols];
	}

	/* fill and print array */
	fill(rows, cols, row_ptrs2);
	printarray(rows, cols, row_ptrs2);

	/* free allocated space */
	free(nums);
	free(row_ptrs2);


	return 0;
}