/in/foo.cc: In function 'int main()':
/in/foo.cc:6:2: warning: 'char* gets(char*)' is deprecated [-Wdeprecated-declarations]
  gets(a);
  ^~~~
In file included from /in/foo.cc:1:0:
/usr/include/stdio.h:640:14: note: declared here
 extern char *gets (char *__s) __wur __attribute_deprecated__;
              ^~~~
/in/foo.cc:6:8: warning: 'char* gets(char*)' is deprecated [-Wdeprecated-declarations]
  gets(a);
        ^
In file included from /in/foo.cc:1:0:
/usr/include/stdio.h:640:14: note: declared here
 extern char *gets (char *__s) __wur __attribute_deprecated__;
              ^~~~
/in/foo.cc:8:2: warning: 'char* gets(char*)' is deprecated [-Wdeprecated-declarations]
  gets(b);
  ^~~~
In file included from /in/foo.cc:1:0:
/usr/include/stdio.h:640:14: note: declared here
 extern char *gets (char *__s) __wur __attribute_deprecated__;
              ^~~~
/in/foo.cc:8:8: warning: 'char* gets(char*)' is deprecated [-Wdeprecated-declarations]
  gets(b);
        ^
In file included from /in/foo.cc:1:0:
/usr/include/stdio.h:640:14: note: declared here
 extern char *gets (char *__s) __wur __attribute_deprecated__;
              ^~~~
/in/foo.cc:9:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i = 0; i<strlen(a); i++)
                 ~^~~~~~~~~~
/in/foo.cc:11:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int k = 0; k<strlen(b); k++)
                  ~^~~~~~~~~~
/in/foo.cc:15:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(int j = i+1;j<strlen(a);j++)
                     ~^~~~~~~~~~
/in/foo.cc:17:7: error: 'j' was not declared in this scope
     a[j-1] = 0;
       ^