How to set the initial state of a matrix in C in special cases?

See more:

C

I'm simulating a square surface that "traps" molecules in C and, I don't know if it's correctly initialized. I want in the beginning of the whole simulation that the grid is totally empty (without any molecule on it) so that it can start to trap the mentioned molecules.

But, when I generate randomly the coordinates of an entry and start checking if the lattice is empty ( to attempt adding molecules to it later on), it seems that every entry the program choose is already "occupied" and I can't see why since I haven't added anything so far.

The following is my code:

What I have tried:

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

//define the dimensions of the latice
#define xmax 2
#define ymax 2

//Define parameters to obtain both the x and y coordinates of a site in the lattice at random
#define LOWER 0 
#define UPPER xmax-1 
#define ALTO ymax-1 
#define CONTAR 1

//we define the Monte Carlo steps
#define MCSS 100

//define the "empty" and "occupied" states
#define empty 0
#define occupied 1


//Function that selects the x-coordinate of the chosen site randomly 
int printrandomx(int lower, int upper, int cuenta)
	{
		int m, num1;
		for (m = 0; m < cuenta ; m++) {
		num1 = (rand() % (upper - lower + 1)) + lower;
		}
	return num1;
	}	

//Function that selects the y-coordinate of the chosen site randomly 
	int printrandomy(int bajo, int alto, int contar)
	{
		int n,num2;
		for (n = 0; n < contar; n++) {
		num2 = (rand() % (alto - bajo + 1)) + bajo;
		}
	return num2;
	}

//Function that generates the random coordinates of a site in the lattice
	int generate_coords(int red[xmax][ymax]){
		int x_coord, y_coord;
		int count = 1;
		for (int i = 0; i < xmax; i++) {
					for (int j = 0; j < ymax; j++) {
						red[i][j] = count++;
						printf("%d ", red[i][j]);
					}
					printf("\n");
				}
	
			x_coord = printrandomx(LOWER, UPPER, CONTAR);
			y_coord = printrandomy(LOWER, ALTO, CONTAR);
			printf("\nSElECTED SITE ---> (x,y)=(%d,%d)\n\n", y_coord, x_coord);

			if (x_coord > xmax || x_coord < 0 || y_coord > ymax || y_coord < 0) {
				printf ("Invalid coordinates given\n");
				return 1;
			}
	}


//Here starts the main function

int main(){
	srand(time(0));
	int x = 0, y = 0;

	//define the grid or lattice we will working with
	int grid[xmax][ymax];
		
	// Initialize lattice to be empty
	for (int i = 0; i < xmax; i++) {
		for (int j = 0; j < ymax; j++) {
			grid[j][i] = empty;
		}
	}
	 
		
	//LOCATE AN ENTRY OF THE MATRIX RANDOMLY
		generate_coords(grid);
			
	//EVALUATE IF THE CHOSEN SITE IS EITHER EMPTY OR OCCUPIED 
	printf("IS IT OCCUPIED???\n\n");			
	if (grid[y][x] == empty){
		printf("It's empty. Let's fill it with a molecule\n\n");
		printf("Here I will specify other conditions :)\n\n");
	}else{ 
			printf("It's occupied, the trial ends. Choose another site again\n\n");
			generate_coords(grid);
	}
	return 0;
}

The chunk of the code that must set the initial array as empty is the following:

// Initialize lattice to be empty
    for (int i = 0; i < xmax; i++) {
        for (int j = 0; j < ymax; j++) {
            grid[j][i] = empty;
        }
    }

However, it doesn't work as expected and I don't know why.