This is a question when setting up an array in a two-dimensional array.

#include <stdio.h>

int main(void){
    int a[20][20] = {};
    int q,i,j,x,y;
    scanf("%d",&q);
    for(i = 0; i < q; i++)
    {
        scanf("%d %d",&x,&y);

        a[x][y] = 1;
    }

    for(i = 1; i < 21; i++)
    {
        for(j = 1; j < 21; j++)
        {
            printf("%d ",a[i][j]);
        }
        printf("\n");
    }

}
//Enter your code here

It's a code to make a checkerboard and set what's on the checkerboard. It's 19*19. But it's 19*19, but when you set the array, you have to set it as a[20][20], so isn't the array 20*20? Another concept says it's created in 2020, but it's created in 1919 I don't understand why this is happening. Some sites have 34 arrays if you set it to 34 I'm so confused that it's set up in 2020 and it's arranged in 1919.