Euler1

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

// This function calculates the sum of all the
// numbers below a certain treshold that are
// a multiple of one of the given numbers.
// argv[1] is the treshold.
// Every argument after is a multiple-number.
// The solution to the problem can be achieved
//  with argv = [10, 3, 5]
int main(int argc, char* argv[]) {
    if (argc < 2) {
        fprintf(stderr, "At least 2 arguments are required.\n");
        return 1;
    }
    uint32_t sum = 0;
    for (char* s_treshhold = argv[1]; *s_treshhold; s_treshhold += 1) {
        if (!(*s_treshhold >= '0' && *s_treshhold <= '9')) {
            fprintf(stderr, "Arguments may only be valid numbers\n");
            return 1;
        }
    }
    uint32_t treshold = strtol(argv[1], NULL, 10);
    uint32_t* mult_args = calloc(argc - 2, sizeof(uint32_t));
    for (int i = 2; i < argc; i += 1) {
        for (char* s_treshhold = argv[i]; *s_treshhold; s_treshhold += 1) {
            if (!(*s_treshhold >= '0' && *s_treshhold <= '9')) {
                fprintf(stderr, "Arguments may only be valid numbers\n");
                free(mult_args);
                return 1;
            }
        }
        mult_args[i-2] = strtol(argv[i], NULL, 10);
    }
    for (int i = 0; i < argc - 2; i += 1) {
        if (mult_args[i] == 0) {
            fprintf(stderr, "Arguments may not be 0.\n");
            return 1;
        }
    }
    for (uint32_t i = 0; i < treshold; i += 1) {
        for (int j = 0; j < argc - 2; j += 1) {
            if (i % mult_args[j] == 0) {
                uint32_t overflow_check = i + sum;
                if (overflow_check < sum) {
                    fprintf(stderr, "An overflow has occured.\n");
                    fprintf(stderr, "Resulting value is at least %u large", UINT32_MAX);
                    free(mult_args);
                    return 1;
                }
                sum += i;
                break; // Break inner loop.
            }
        }
    }
    printf("The sum of all multiples of [");
    for (int i = 0; i < argc - 3; i += 1) {
        printf("%d,", mult_args[i]);
    }
    printf("%u] below %u is: %u.\n", mult_args[argc - 3], treshold, sum);
    free(mult_args);
    return 0;
}