foo.cc: In function 'void Concat(char*, char*)':
foo.cc:9:22: warning: comparison of integer expressions of different signedness: 'int' and 'size_t' {aka 'long unsigned int'} [-Wsign-compare]
    9 |         for(int i=1;i<strlen(s2);i++)
      |                     ~^~~~~~~~~~~
foo.cc: In function 'int main()':
foo.cc:16:9: warning: 'char* gets(char*)' is deprecated [-Wdeprecated-declarations]
   16 |     gets(s1);
      |     ~~~~^~~~
In file included from /nix/store/jgdz5wfqc6q6qhy17lsqnfpbkfi1fcar-gcc-12.2.0/include/c++/12.2.0/cstdio:42,
                 from stdc++.h:46:
/nix/store/linb70pgp53f0kygxm5wk163dx22d681-glibc-2.37-45-dev/include/stdio.h:605:14: note: declared here
  605 | extern char *gets (char *__s) __wur __attribute_deprecated__;
      |              ^~~~
foo.cc:17:9: warning: 'char* gets(char*)' is deprecated [-Wdeprecated-declarations]
   17 |     gets(s2);
      |     ~~~~^~~~
/nix/store/linb70pgp53f0kygxm5wk163dx22d681-glibc-2.37-45-dev/include/stdio.h:605:14: note: declared here
  605 | extern char *gets (char *__s) __wur __attribute_deprecated__;
      |              ^~~~
/nix/store/3r87a2wq1w4l66wnsm7rqvy608mx23h6-binutils-2.40/bin/ld: /tmp/ccTmg9FO.o: in function `main':
foo.cc:(.text.startup+0x44): warning: the `gets' function is dangerous and should not be used.

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