foo.cc: In function 'int main()':
foo.cc:10:10: 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/c++/7/ext/string_conversions.h:43,
                 from /usr/include/c++/7/bits/basic_string.h:6361,
                 from /usr/include/c++/7/string:52,
                 from /usr/include/c++/7/bits/locale_classes.h:40,
                 from /usr/include/c++/7/bits/ios_base.h:41,
                 from /usr/include/c++/7/ios:42,
                 from /usr/include/c++/7/ostream:38,
                 from /usr/include/c++/7/iostream:39,
                 from foo.cc:1:
/usr/include/x86_64-linux-gnu/bits/stdio2.h:232:1: note: declared here
 gets (char *__str)
 ^~~~
foo.cc:20:19: warning: format '%f' expects argument of type 'double', but argument 2 has type 'int' [-Wformat=]
    printf("%.2f",n);
                   ^
foo.cc:8:12: warning: unused variable 'a' [-Wunused-variable]
    int sum,a,x,i,n;
            ^
foo.cc:10:8: warning: ignoring return value of 'char* gets(char*)', declared with attribute warn_unused_result [-Wunused-result]
    gets(s);
    ~~~~^~~
foo.cc:8:18: warning: 'n' may be used uninitialized in this function [-Wmaybe-uninitialized]
    int sum,a,x,i,n;
                  ^
foo.cc:19:6: warning: 'x' may be used uninitialized in this function [-Wmaybe-uninitialized]
    n=(float)x/sum*100;
      ^~~~~~~~
/tmp/cczdgnXT.o: In function `main':
foo.cc:(.text.startup+0x22): warning: the `gets' function is dangerous and should not be used.

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