foo.cc: In function 'int main()':
foo.cc:6:10: warning: right operand of comma operator has no effect [-Wunused-value]
  cin>>a,b;
          ^
foo.cc:7:7: error: expected ';' before 'a'
  cout a+b <<endl; 
       ^
foo.cc:7:17: warning: statement has no effect [-Wunused-value]
  cout a+b <<endl; 
                 ^

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