1. C character strings and string functions

In C, character strings are just arrays of characters, with a terminating zero byte marking the end of the string.

This implies that you can not put a zero byte in the middle of a string;

you can, but the standard library functions will treat the first zero byte as the end of the string.

Example:
        char s[80] = { 'a', 'b', 'c', '\0', 'd', 'e', 'f', '\0' }
or
        char s[80] = "abc\0def";

strlen(s) will return 3.

There is not much you can do with strings in C without using the standard library string functions.

For example, to change the value of the string s above you can not do:

        s = "xyz"; /* illegal */

because C does not copy arrays (except, of course, in an initialization part of a declaration).

But you could do either:

        s[0] = 'x';  s[1] = 'y';  s[2] = 'z';  s[3] = '\0';
or
        strcpy( s, "xyz");

Note that the illegal statement above would be legal if the left-hand side was a pointer:

        char *p;

        p = "xyz";      /* OK */

because, in this case, the array of characters "xyz" is not copied,

only the address of that array is assigned to p.