foo.c: In function 'Concat':
foo.c:6:2: warning: this 'while' clause does not guard... [-Wmisleading-indentation]
    6 |  while(str[i]!='\0')
      |  ^~~~~
foo.c:8:3: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the 'while'
    8 |   a[0]=str[i-2];
      |   ^
foo.c: In function 'main':
foo.c:15:2: warning: 'gets' is deprecated [-Wdeprecated-declarations]
   15 |  gets(s1);
      |  ^~~~
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:16:2: warning: 'gets' is deprecated [-Wdeprecated-declarations]
   16 |  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: In function 'Concat':
foo.c:11:1: warning: control reaches end of non-void function [-Wreturn-type]
   11 | }
      | ^
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);
      |  ^~~~~~~~
foo.c:16:2: warning: ignoring return value of 'gets', declared with attribute warn_unused_result [-Wunused-result]
   16 |  gets(s2);
      |  ^~~~~~~~
foo.c: In function 'Concat':
foo.c:6:11: warning: 'i' is used uninitialized in this function [-Wuninitialized]
    6 |  while(str[i]!='\0')
      |           ^
/usr/bin/ld: /tmp/ccfVpHp4.o: in function `main':
foo.c:(.text.startup+0x4e): warning: the `gets' function is dangerous and should not be used.

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