foo.c: In function 'main':
foo.c:13:2: warning: 'gets' is deprecated [-Wdeprecated-declarations]
  gets(a);
  ^~~~
In file included from /usr/include/stdio.h:862:0,
                 from foo.c:1:
/usr/include/x86_64-linux-gnu/bits/stdio2.h:232:1: note: declared here
 gets (char *__str)
 ^~~~
foo.c:13:2: warning: ignoring return value of 'gets', declared with attribute warn_unused_result [-Wunused-result]
  gets(a);
  ^~~~~~~
foo.c:63:22: warning: 'm' may be used uninitialized in this function [-Wmaybe-uninitialized]
  gs = (len-i-1)*(i+1)+i+1;
       ~~~~~~~~~~~~~~~^~
foo.c:7:12: note: 'm' was declared here
     int t, m;
            ^
/tmp/ccYPJ9JO.o: In function `main':
foo.c:(.text.startup+0x2d): warning: the `gets' function is dangerous and should not be used.

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