foo.cpp: In function 'void extern_str(char*, int)':
foo.cpp:13:34: error: 'isdigit' was not declared in this scope
     int mztj = isdigit(buf[l - 1]) && isdigit(buf[l + 1]) || isalpha(buf[l - 1]) && isalpha(buf[l + 1]);
                                  ^
foo.cpp:13:80: error: 'isalpha' was not declared in this scope
     int mztj = isdigit(buf[l - 1]) && isdigit(buf[l + 1]) || isalpha(buf[l - 1]) && isalpha(buf[l + 1]);
                                                                                ^
foo.cpp:32:32: error: 'toupper' was not declared in this scope
     if(p1 == 2) sc = toupper(sc), ec = toupper(ec);
                                ^
foo.cpp:43:32: warning: array subscript has type 'char' [-Wchar-subscripts]
             printf("%c", lstr[i]);
                                ^
foo.cpp:47:32: warning: array subscript has type 'char' [-Wchar-subscripts]
             printf("%c", lstr[i]);
                                ^