/in/foo.c:5:1: error: unknown type name 'class'
 class Stack
 ^~~~~
/in/foo.c:6:1: error: expected '=', ',', ';', 'asm' or '__attribute__' before '{' token
 {
 ^
/in/foo.c: In function 'Match':
/in/foo.c:30:2: error: unknown type name 'Stack'
  Stack s;
  ^~~~~
/in/foo.c:31:6: warning: unused variable 'length' [-Wunused-variable]
  int length=strlen(str);
      ^~~~~~
/in/foo.c:30:8: warning: unused variable 's' [-Wunused-variable]
  Stack s;
        ^
/in/foo.c: In function 'main':
/in/foo.c:48:2: warning: 'gets' is deprecated [-Wdeprecated-declarations]
  gets(str);
  ^~~~
In file included from /in/foo.c:1:0:
/usr/include/stdio.h:640:14: note: declared here
 extern char *gets (char *__s) __wur __attribute_deprecated__;
              ^~~~