strcat, strncat - concatenate two strings
char *strcat(char *dest, const char *src);
char *strncat(char *dest, const char *src, size_t n);
The strcat() function appends the src string to the dest
string overwriting the `\0' character at the end of dest, and then adds
a terminating `\0' character. The strings may not overlap, and the dest
string must have enough space for the result.
The strncat() function is similar, except that only the
first n characters of src are appended to dest.
The strcat() and strncat() functions return a pointer to the
resulting string dest.
SVID 3, POSIX, BSD 4.3, ISO 9899