foo.cc: In function 'int main()':
foo.cc:14:10: warning: unused variable 'j' [-Wunused-variable]
  int n,i,j,M=0,F=0;
          ^
foo.cc:15:8: warning: unused variable 'msum' [-Wunused-variable]
  float msum,fsum,sum;
        ^~~~
foo.cc:15:13: warning: unused variable 'fsum' [-Wunused-variable]
  float msum,fsum,sum;
             ^~~~
foo.cc:15:18: warning: unused variable 'sum' [-Wunused-variable]
  float msum,fsum,sum;
                  ^~~
foo.cc:20:8: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d%s%d%f",&s[i].sno,s[i].sname,&s[i].sex,&s[i].score);
   ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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