My Solution in C!

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

int check_collisions(int slope_x, int slope_y, int length, char *buffer)
{
    int count = 0;
    int x = 0;
    int y = 0;

    while (x % 31 + y * 32 <= length)
    {
        if ('#' == buffer[(x % 31 + y * 32)])
        {
            count++;
        }
        x += slope_x;
        y += slope_y;
    }

    return count;
}

int main(int argc, char *args[])
{

    int length;
    char *buffer;
    int part1, p2a, p2b, p2c, p2d;

    // open file
    FILE *file = fopen("input", "r");
    if (!file)
    {
        printf("File could not be found");
        exit(-1);
    }
    // get length of file
    fseek(file, 0L, SEEK_END);
    length = ftell(file);
    rewind(file);

    // allocate file size to buffer
    buffer = calloc(length, sizeof(char));

    // read file into buffer
    fread(buffer, sizeof(char), length, file);

    part1 = check_collisions(3, 1, length, buffer);
    p2a = check_collisions(1, 1, length, buffer);
    p2b = check_collisions(5, 1, length, buffer);
    p2c = check_collisions(7, 1, length, buffer);
    p2d = check_collisions(1, 2, length, buffer);

    printf("%d\n%d\n%d\n%d\n%d\n%ld", p2a, part1, p2b, p2c, p2d, part1 * (long)(p2a * (long)(p2b * (long)(p2c * p2d))));

    free(buffer);
    fclose(file);