/in/foo.cc: In function 'void cheng(int)':
/in/foo.cc:29:7: warning: statement has no effect [-Wunused-value]
  for(i;i>=1;i--)
       ^
/in/foo.cc: In function 'int main()':
/in/foo.cc:35:2: warning: 'char* gets(char*)' is deprecated [-Wdeprecated-declarations]
  gets(ma);
  ^~~~
In file included from /usr/include/c++/6/cstdio:42:0,
                 from /usr/include/x86_64-linux-gnu/c++/6/bits/stdc++.h:46,
                 from /in/foo.cc:1:
/usr/include/stdio.h:640:14: note: declared here
 extern char *gets (char *__s) __wur __attribute_deprecated__;
              ^~~~
/in/foo.cc:35:9: warning: 'char* gets(char*)' is deprecated [-Wdeprecated-declarations]
  gets(ma);
         ^
In file included from /usr/include/c++/6/cstdio:42:0,
                 from /usr/include/x86_64-linux-gnu/c++/6/bits/stdc++.h:46,
                 from /in/foo.cc:1:
/usr/include/stdio.h:640:14: note: declared here
 extern char *gets (char *__s) __wur __attribute_deprecated__;
              ^~~~
/in/foo.cc:36:5: warning: 'char* gets(char*)' is deprecated [-Wdeprecated-declarations]
     gets(mb);
     ^~~~
In file included from /usr/include/c++/6/cstdio:42:0,
                 from /usr/include/x86_64-linux-gnu/c++/6/bits/stdc++.h:46,
                 from /in/foo.cc:1:
/usr/include/stdio.h:640:14: note: declared here
 extern char *gets (char *__s) __wur __attribute_deprecated__;
              ^~~~
/in/foo.cc:36:12: warning: 'char* gets(char*)' is deprecated [-Wdeprecated-declarations]
     gets(mb);
            ^
In file included from /usr/include/c++/6/cstdio:42:0,
                 from /usr/include/x86_64-linux-gnu/c++/6/bits/stdc++.h:46,
                 from /in/foo.cc:1:
/usr/include/stdio.h:640:14: note: declared here
 extern char *gets (char *__s) __wur __attribute_deprecated__;
              ^~~~
/in/foo.cc:34:8: warning: unused variable 'n' [-Wunused-variable]
  int i,n,m,lena,lenb,lenc,j;
        ^
/in/foo.cc:34:10: warning: unused variable 'm' [-Wunused-variable]
  int i,n,m,lena,lenb,lenc,j;
          ^
/in/foo.cc:34:22: warning: unused variable 'lenc' [-Wunused-variable]
  int i,n,m,lena,lenb,lenc,j;
                      ^~~~
/in/foo.cc:34:27: warning: unused variable 'j' [-Wunused-variable]
  int i,n,m,lena,lenb,lenc,j;
                           ^
/tmp/cclfc4oF.o: In function `main':
foo.cc:(.text.startup+0xc): warning: the `gets' function is dangerous and should not be used.