foo.cc: In function 'int main()':
foo.cc:38:9: warning: 'char* gets(char*)' is deprecated [-Wdeprecated-declarations]
   gets(s);
         ^
In file included from /usr/include/stdio.h:862:0,
                 from /usr/include/c++/7/cstdio:42,
                 from /usr/include/x86_64-linux-gnu/c++/7/bits/stdc++.h:46,
                 from foo.cc:1:
/usr/include/x86_64-linux-gnu/bits/stdio2.h:232:1: note: declared here
 gets (char *__str)
 ^~~~
foo.cc:31:14: warning: unused variable 'ch' [-Wunused-variable]
  char s[100],ch;
              ^~
foo.cc:32:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d%d\n",&m,&n);
  ~~~~~^~~~~~~~~~~~~~~~
foo.cc:38:7: warning: ignoring return value of 'char* gets(char*)', declared with attribute warn_unused_result [-Wunused-result]
   gets(s);
   ~~~~^~~
/tmp/ccDvrD1g.o: In function `main':
foo.cc:(.text.startup+0xc1): warning: the `gets' function is dangerous and should not be used.

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