XOR-Encryption works on Code blocks not on Visual Studio 2017

Question

so I would like to encrypt my data when write into .txt file so I choose XOR-Encryption from this code: Github So when I run in code blocks it runs and shows this result:

Encrypted: :=.43*-:8m2$.a
Decrypted:kylewbanks.com0

Process returned 0 (0x0)   execution time : 0.025 s
Press any key to continue.

But When I start use Visual Studio 2017 it shows this error:

Error (active)  E0059   function call is not allowed in a constant expression   

Which means I cant put variable when declaring an array, so is there any method for my encryption to work in VS2017. I think the problems is when declare the variable using constant, anyway to force it or other encryption method that is easy to use, I wont need to be secure just to prevent plain text in file. Anyway this is the only code:

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

void encryptDecrypt(char *input, char *output) {
    char key[] = {'K', 'C', 'Q'}; //Can be any chars, and any size array

    int i;
    for(i = 0; i < strlen(input); i++) {
        output[i] = input[i] ^ key[i % (sizeof(key)/sizeof(char))];
    }
}

int main () {
    char baseStr[] = "kylewbanks.com";

    char encrypted[strlen(baseStr)];
    encryptDecrypt(baseStr, encrypted);
    printf("Encrypted:%s\n", encrypted);

    char decrypted[strlen(baseStr)];
    encryptDecrypt(encrypted, decrypted);
    printf("Decrypted:%s\n", decrypted);
}

Answer 1

MSVC does not support Variable Length Arrays. One way round is to allocate the memory.

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

void encryptDecrypt(char *input, char *output) {
    char key[] = {'K', 'C', 'Q'}; //Can be any chars, and any size array
    size_t i;
    for(i = 0; i < strlen(input); i++) {
        output[i] = input[i] ^ key[i % (sizeof(key)/sizeof(char))];
    }
    output[i] = '\0';               // terminate
}

int main () {
    char baseStr[] = "kylewbanks.com";
    size_t len = strlen(baseStr) + 1;

    char *encrypted = malloc(len);
    if(encrypted == NULL) {
        // error handling
    }
    encryptDecrypt(baseStr, encrypted);
    printf("Encrypted:%s\n", encrypted);

    char *decrypted = malloc(len);
    if(decrypted == NULL) {
        // error handling
    }
    encryptDecrypt(encrypted, decrypted);
    printf("Decrypted:%s\n", decrypted);

    free(decrypted);
    free(encrypted);
}

Please note that an extra byte is needed for the string terminator - and the string should be terminated.