char *jystr(char jy，char *str，int jynum)； That's right.

Parameter corresponding to formal parameter jy must be of char type; The second parameter is a pointer type parameter, the argument must be an array type or a pointer type, and the parameter participates in the common storage unit; The argument corresponding to the third formal parameter jynum must be character type (which can be used as plastic in C language) or plastic.

The function type is a pointer type, that is, the return value is a pointer to character data.