_CP_str is equivalent to the result = str(string, expression) BASIC statement.
int _CP_str(CPSTR** result, CPSTR* string, int expression)
This function returns -1 if an error occurs. The error code is contained in _CP_errno.
/* Prints "aaa". */
CPSTR * s = _CP_mkstr("a");
_CP_str(&s,s,3);
_CP_print(s);