foo.cc: In function 'int main()':
foo.cc:6:2: error: 'cin' was not declared in this scope
    6 |  cin>>a;
      |  ^~~
foo.cc:2:1: note: 'std::cin' is defined in header '<iostream>'; did you forget to '#include <iostream>'?
    1 | #include <stdio.h>
  +++ |+#include <iostream>
    2 | using namespace std;
foo.cc:7:2: error: 'cout' was not declared in this scope
    7 |  cout<<a*a;
      |  ^~~~
foo.cc:7:2: note: 'std::cout' is defined in header '<iostream>'; did you forget to '#include <iostream>'?
foo.cc: At global scope:
foo.cc:9:1: error: expected unqualified-id before 'return'
    9 | return 0;
      | ^~~~~~

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