foo.c: In function 'main':
foo.c:6:9: error: 'cin' undeclared (first use in this function)
    6 |         cin>>a>>b;
      |         ^~~
foo.c:6:9: note: each undeclared identifier is reported only once for each function it appears in
foo.c:7:9: error: 'cout' undeclared (first use in this function)
    7 |         cout<<a<<b<<endl;
      |         ^~~~
foo.c:7:21: error: 'endl' undeclared (first use in this function)
    7 |         cout<<a<<b<<endl;
      |                     ^~~~

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