foo.cc: In function 'int main()':
foo.cc:7:12: error: 'a' cannot be used as a function
    7 |     c=a(a+b)*2;
      |            ^
foo.cc:9:12: error: expected ';' before string constant
    9 |     cout<<c" "<<d;
      |            ^~~
      |            ;

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