adventofcode/2020/2/parse2.c

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

int main(void) {
	FILE *fp;
	char line[255];
	int valid = 0;

	fp = fopen("input", "r");

	if(fp == NULL) {
		perror("Error opening file.");
		return(-1);
	}

	while(fgets(line, sizeof(line), fp) != NULL) {
		int start, end;
		char subject;
		char password[64];

		sscanf(line, "%d-%d %c: %s\n", &start, &end, &subject, password);
	
		if(password[start - 1] == subject && password[end - 1] != subject ||
			password[end - 1] == subject && password[start - 1] != subject)
			valid++;
	}

	fclose(fp);

	printf("There are %d valid passwords\n", valid);
}