foo.c: In function 'Concat':
foo.c:8:11: error: 'i' undeclared (first use in this function)
    8 |         t[i+tlen]=0;
      |           ^
foo.c:8:11: note: each undeclared identifier is reported only once for each function it appears in
foo.c: In function 'main':
foo.c:14:9: warning: 'gets' is deprecated [-Wdeprecated-declarations]
   14 |         gets(s1);
      |         ^~~~
In file included from foo.c:1:
/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.c:15:9: warning: 'gets' is deprecated [-Wdeprecated-declarations]
   15 |         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__;
      |              ^~~~

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