Why am I getting segmentation fault (core dumped), and what does it mean?

Question

I am trying to run this piece of code where I get input "message" from a user and I turn that message to binary code. I later print this as lit bulbs for 1 and dark ones for 0 with emojis. However, I keep getting 'segmentation fault (core dumped)' after I enter my input on the terminal. Does anyone know why, and what does it mean in this particular case? Thank you!

int main(void)
{
    // prompt for message
    string message = get_string("message: ");
    int len = strlen(message);

    for (int i = 0; i < len; i++)
    {
        int value = message[i];
        int binary_code[BITS_IN_BYTE];

        // convert to binary
        for (int j = 0; j < BITS_IN_BYTE; j++)
        {
            int rem;
            int place = BITS_IN_BYTE - j;
            rem = value % 2;
            binary_code[place] = rem;
            value /= 2;
        }

        // print bulbs
        for (int k = 0; k < BITS_IN_BYTE; k++)
        {
            print_bulb(binary_code[k]);
        }
        printf("\n");
    }
}

Answer 1

At least there is the following problem with your code.

You declared an array with BITS_IN_BYTE elements

int binary_code[BITS_IN_BYTE];

So the valid range of indices is [0, BITS_IN_BYTE).

However when j is equal to 0 in this for loop

    for (int j = 0; j < BITS_IN_BYTE; j++)
    {
        int rem;
        int place = BITS_IN_BYTE - j;
        rem = value % 2;
        binary_code[place] = rem;
        value /= 2;
    }

then the value of the variable place is equal to BITS_IN_BYTE

int place = BITS_IN_BYTE - j;

As a result this statement

binary_code[place] = rem;

writes to memory outside the array that results in undefined behavior.

You should initialize the variable place the following way

int place = BITS_IN_BYTE - j - 1;