foo.c: In function 'main':
foo.c:6:3: error: 'cin' undeclared (first use in this function)
    6 |   cin>>a>>b;
      |   ^~~
foo.c:6:3: note: each undeclared identifier is reported only once for each function it appears in
foo.c:7:2: error: 'cout' undeclared (first use in this function)
    7 |  cout<<b<<","<<a;
      |  ^~~~

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