/in/foo.c: In function 'main':
/in/foo.c:7:5: warning: 'gets' is deprecated [-Wdeprecated-declarations]
     gets(a);
     ^~~~
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__;
              ^~~~
/in/foo.c:8:2: warning: 'gets' is deprecated [-Wdeprecated-declarations]
  gets(b);
  ^~~~
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__;
              ^~~~
/in/foo.c: In function 'Concat':
/in/foo.c:19:23: warning: left-hand operand of comma expression has no effect [-Wunused-value]
  for(i=n-1,j=1;i<m+n-2,j<m;i++,j++)
                       ^
/tmp/cct10NFb.o: In function `main':
foo.c:(.text.startup+0x15): warning: the `gets' function is dangerous and should not be used.