blurred vision 더블릿

#include <stdio.h>
 
int arr[20][20] = { 0 };
 
int main() {
    char stend[10];
    int a, b;
    scanf("%s %d %d", stend, &a, &b);
 
    for(int j = 0 ; j < a ; j++) {
        char num[20] = { 0 };
        scanf("%s", num);
        for (int i = 0; i < b; i++) {
            arr[j][i] = (int)(num[i] - '0');
        }
    }
    scanf("%s", stend);
 
    for (int i = 0; i < a - 1; i++) {
        for (int j = 0; j < b - 1; j++) {
            arr[i][j] = (arr[i][j] + arr[i+1][j] + arr[i][j+1] +
                arr[i+1][j+1]) / 4;
            printf("%d", arr[i][j]);
        }
        printf("\n");
    }
}