foo.cc: In function 'int main()':
foo.cc:7:10: error: 'a' was not declared in this scope
     cin>>a;
          ^
foo.cc:8:8: error: expected primary-expression before '{' token
  cout<<{}
        ^
foo.cc:9:7: error: expected primary-expression before '{' token
 cout<<{1}
       ^
foo.cc:10:7: error: expected primary-expression before '{' token
 cout<<{2}
       ^
foo.cc:11:7: error: expected primary-expression before '{' token
 cout<<{1,2}
       ^
foo.cc:12:7: error: expected primary-expression before '{' token
 cout<<{3}
       ^
foo.cc:13:7: error: expected primary-expression before '{' token
 cout<<{1,3}
       ^
foo.cc:14:7: error: expected primary-expression before '{' token
 cout<<{2,3}
       ^
foo.cc:15:7: error: expected primary-expression before '{' token
 cout<<{1,2,3}
       ^

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