aoc-2020/3.c

#include "stdio.h"

int tree_count(char[323][31], int, int);

int main() {
    char lines[323][31];

    int i = 0;
    while (scanf("%s", lines[i++]) == 1)
        ;

    long product = 1;
    product *= tree_count(lines, 3, 1);
    printf("Answer 1: %ld\n", product);

    product *= tree_count(lines, 1, 1);
    product *= tree_count(lines, 5, 1);
    product *= tree_count(lines, 7, 1);
    product *= tree_count(lines, 1, 2);

    printf("Answer 2: %ld\n", product);
}

int tree_count(char lines[323][31], int x_inc, int y_inc) {

    int x = 0, y = 0;
    int trees = 0;

    while (y < 323) {
        if (lines[y][x] == '#')
            trees++;

        y += y_inc; x += x_inc;
        x %= 31;
    }

    return trees;
}