printf printing an @ after a string

Question

When I try to print an array of characters as a string with a variable before, like that

int main()
{
    string text = "a";
    char str[2] = {'a', 'b'};
    printf("%s\n", str);
}

I get this output ab @ and I don't have ANY idea where this @ came from. It's bugging my "substitution.c" from pset2

Answer 1

From man printf

s

If no l modifier is present: The const char * argument is expected to be a pointer to an array of character type (pointer to a string). Characters from the array are written up to (but not including) a terminating null byte ('\0');....

A char array cannot be treated as a string (char *) unless it has a terminating null byte (\0). (I don't recall if this topic has been discussed at this point in the courseware). The @ comes from the memory after str and before a null byte is encountered.

One option in substitution is to print each char (with %c directive) as it is ciphered.