foo.cc: In function 'int main()':
foo.cc:7:2: error: 'cin' was not declared in this scope
    7 |  cin>>n;
      |  ^~~
foo.cc:3:1: note: 'std::cin' is defined in header '<iostream>'; did you forget to '#include <iostream>'?
    2 | #include<cmath>
  +++ |+#include <iostream>
    3 | using  namespace  std;
foo.cc:8:2: error: 'cout' was not declared in this scope
    8 |  cout<<n<<"-->";
      |  ^~~~
foo.cc:8:2: note: 'std::cout' is defined in header '<iostream>'; did you forget to '#include <iostream>'?
foo.cc:6:8: warning: unused variable 'i' [-Wunused-variable]
    6 |  int n,i,j;
      |        ^
foo.cc:6:10: warning: unused variable 'j' [-Wunused-variable]
    6 |  int n,i,j;
      |          ^

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