Умножение кубов(алгоритм Рота)

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

char* umnoz(char* el1, char* el2){
    int length = strlen(el1);
    char *res = (char*) calloc(30, sizeof (char));
    for (int i = 0; i < length; ++i) {
        if(el1[i] == el2[i]){
            res[i] = el1[i];
        } else if(el1[i] != el2[i] && el1[i] != 'x' && el2[i] != 'x'){
            res[i] = 'y';
        } else if(el1[i] != el2[i] && (el1[i] == 'x' || el2[i] != 'x')){
            res[i] = el2[i];
        } else if(el1[i] != el2[i] && (el1[i] != 'x' || el2[i] == 'x')){
            res[i] = el1[i];
        }
    }
    return res;
}

int main() {
    int amount;

    printf("enter amount of elements\n");
    scanf("%d", &amount);

    char* elements[amount];
    char* table[amount][amount];

    for (int i = 0; i < amount; ++i) {
        elements[i] = (char*) calloc(50, sizeof (char));
    }

    getchar();
    for (int i = 0; i < amount; ++i) {
        printf("enter element #%d\n", i + 1);
        fflush(stdin);
        gets(elements[i]);
    }

    for (int i = 0; i < amount; ++i) {
        for (int j = 0; j < amount; ++j) {
            table[i][j] = (char*) calloc(50, sizeof (char));
        }
    }

    for (int i = 0; i < amount; ++i) {
        for (int j = 0; j < amount; ++j) {
            table[i][j] = umnoz(elements[i], elements[j]);
        }
    }

    for (int i = 0; i < amount; ++i) {
        for (int j = i; j < amount; ++j) {
            table[i][j] = "-----";
        }
    }

    for (int i = 0; i < amount; ++i) {
        printf("%s:\t", elements[i]);
        for (int j = 0; j < amount; ++j) {
            printf("%s\t", table[i][j]);
        }
        printf("\n-----------------------------------------\n");
    }


    return 0;
}