Can't print/populate a string in C

Question

In PSET2 Substitution, to display the results, I'm initializing an empty string with:

    char cyphertext[] = {'\0'};

Populating it with:

// makes the substitution
    for (int i = 0; text[i] != 0 ; i++)
    {
        if (isupper(text[i]))
        {
            cyphertext[i] = text[i] - 'A';
        } else {
            cyphertext[i] = text[i] - 'a';
        }
    }

But when I try to print it with:

printf("cyphertext: %s\n", cyphertext);

I get:

cyphertext: 

            �

I don't know where I'm making a mistake. Am I declaring it wrong? Am I "filling" it wrong? Am I printing it wrong?

Answer 1

The first problem is the declaration. When a string (a char array) is declared, the space for it is allocated in memory. In this case, it's initialized as containing only the end of string (EOS) marker, "\0", so only one space is allocated to it. Any attempt to insert any string into it will overwrite the physical memory adjacent to it. Instead, if you had declared it with an actual length, like this:

char cyphertext[strlen(something appropriate) +1 ] = {'\0'};

then the right amount of memory would have been allocated.

Next, the code isn't encoding the letters correctly. It's producing non-printable or non-alphanumeric ASCII characters. I suggest that a review of the videos on the encoding should be made.

Also, what will the code do with non-alpha characters like punctuation, numbers or spaces?

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