/in/foo.c: In function 'main':
/in/foo.c:5:2: warning: 'gets' is deprecated [-Wdeprecated-declarations]
  gets(s1)!='\0';
  ^~~~
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:5:10: warning: value computed is not used [-Wunused-value]
  gets(s1)!='\0';
  ~~~~~~~~^~~~~~
/in/foo.c:6:2: warning: 'gets' is deprecated [-Wdeprecated-declarations]
  gets(s2)!='\0';
  ^~~~
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:6:10: warning: value computed is not used [-Wunused-value]
  gets(s2)!='\0';
  ~~~~~~~~^~~~~~
/in/foo.c:7:5: warning: implicit declaration of function 'strlen' [-Wimplicit-function-declaration]
  s1[strlen(s1)-1]=0;
     ^~~~~~
/in/foo.c:7:5: warning: incompatible implicit declaration of built-in function 'strlen'
/in/foo.c:7:5: note: include '<string.h>' or provide a declaration of 'strlen'
/in/foo.c:8:2: warning: implicit declaration of function 'strcat' [-Wimplicit-function-declaration]
  strcat(s1,s2+1);
  ^~~~~~
/in/foo.c:8:2: warning: incompatible implicit declaration of built-in function 'strcat'
/in/foo.c:8:2: note: include '<string.h>' or provide a declaration of 'strcat'
/tmp/ccbUCzA8.o: In function `main':
foo.c:(.text.startup+0x18): warning: the `gets' function is dangerous and should not be used.