sum1.c

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

int main()
{
    const size_t size = 1000;
    char *line;
    FILE *infile;
    double a, b, c, sum;

    line = malloc(size);
    if (line == NULL)
    {
        printf("Out of memory!\n");
        return 1;
    }

    infile = fopen("input.txt", "rt");
    if (infile == NULL)
    {
        printf("Cannot open input file.\n");
        free(line);
        return 1;
    }

    sum = 0.0;
    while (fgets(line, size, infile))
    {
        if (3 != sscanf(line, "%lf %lf %lf", &a, &b, &c))
        {
            printf("BAD INPUT\n");
            fclose(infile);
            free(line);
            return 1;
        }
        sum += a * b * c;
    }

    fclose(infile);
    free(line);
    printf("SUM=%lf\n", sum);
    return 0;
}