foo.c: In function 'main':
foo.c:15:2: warning: 'gets' is deprecated [-Wdeprecated-declarations]
   15 |  gets(s1);gets(s2);
      |  ^~~~
In file included from /usr/include/stdio.h:867,
                 from foo.c:1:
/usr/include/x86_64-linux-gnu/bits/stdio2.h:235:1: note: declared here
  235 | gets (char *__str)
      | ^~~~
foo.c:15:2: warning: 'gets' is deprecated [-Wdeprecated-declarations]
   15 |  gets(s1);gets(s2);
      |  ^~~~
In file included from /usr/include/stdio.h:867,
                 from foo.c:1:
/usr/include/x86_64-linux-gnu/bits/stdio2.h:235:1: note: declared here
  235 | gets (char *__str)
      | ^~~~
foo.c:18:2: error: too many arguments to function 'Concat'
   18 |  Concat(s1,s2,m1,m2);
      |  ^~~~~~
foo.c:3:5: note: declared here
    3 | int Concat(char str1[],char str2[])
      |     ^~~~~~
foo.c: In function 'Concat':
foo.c:10:1: warning: control reaches end of non-void function [-Wreturn-type]
   10 | }
      | ^
foo.c: In function 'main':
foo.c:15:2: warning: ignoring return value of 'gets', declared with attribute warn_unused_result [-Wunused-result]
   15 |  gets(s1);gets(s2);
      |  ^~~~~~~~
foo.c:15:11: warning: ignoring return value of 'gets', declared with attribute warn_unused_result [-Wunused-result]
   15 |  gets(s1);gets(s2);
      |           ^~~~~~~~

[Hydro](https://hydro.ac)提供评测服务