foo.cc: In function 'int main()':
foo.cc:6:10: warning: right operand of comma operator has no effect [-Wunused-value]
    6 |  cin>>a,b;
      |          ^
foo.cc:7:13: error: 'b' cannot be used as a function
    7 |  cout<<b(a+b)/2;
      |             ^

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