adventofcode/2020/2/parse.c

#include <stdio.h>
#include <stdlib.h>
#include <string.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);

		int occ = 0;
		for(int i=0; password[i]; i++) 
			if(password[i] == subject) occ++;
		
		if(occ <= end && occ >= start) valid++;
	}

	fclose(fp);

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