Pointer Arrays: Pointers to Pointers
says that lineptr is an array of MAXLINES elements, each element of which is a pointer to a char. That is, lineptr [i] is a character pointer, and *lineptr[i] is the character it points to, the first character of the i-th saved text line.
Since lineptr is itself the name of an array, it can be treated as a pointer in the same manner as in our earlier examples, and writelines can be written instead as
/* writelines: write output lines */
void writelines(char *lineptr, int nlines)
while (nlines-- > 0)
Initially *lineptr points to the first line; each increment advances it to the next line pointer while nlines is counted down.
[The C Programming Language p.109]