Project Euler #13

q13.c

/*
 * Project Euler #13
 * Eugene Ma
 *
 * Real Answer: 5537376230
 */

#include <stdio.h>
#include <string.h>

#define LINES 100
#define DIGITS 50      

char numbers[LINES][DIGITS];

int sum_digits(int n);

int main(void) {
        FILE *fp;
        int i, j;
        int sum;
        int carry = 0;
        int digits[10];

        fp = fopen("input.txt", "r");
        if (fp == NULL) {
                perror("fopen");
                return -1;
        }

        for (i = 0; i < LINES; i++) {
                char buf[52]; /* '\n', '\0' */
                if (fgets(buf, sizeof(buf), fp) == NULL) {
                        fclose(fp);
                        perror("fgets");
                        return -1;
                }
                strncpy(numbers[i], buf, DIGITS);
                for (j = 0; j < DIGITS; j++)
                        numbers[i][j] -= '0';
        }
        fclose(fp);

        for (i = DIGITS-1; i >= 0; i--) {
                sum = sum_digits(i) + carry;
                carry = sum/10;
                digits[i%10] = sum % 10;
        }

        /* The first few digits are carry digits */
        printf("%d", carry);

        /* Calculate number of carry digits */
        for (j = 0; carry > 0; j++, carry /= 10)
                ;

        /* Print the rest */
        for (i = 0; i < 10-j; i++)
                printf("%d", digits[i]);
        printf("\n");

        return 0;
}

int sum_digits(int n) {
        int i, sum = 0;

        for (i = 0; i < LINES; i++)
                sum += numbers[i][n];
        return sum;
}