View Compilation Error

0_0_30756079_8854.cpp: In function 'std::pair<int, int> sum(std::pair<int, int>, std::pair<int, int>)':
0_0_30756079_8854.cpp:10:35: error: expression list treated as compound expression in initializer [-fpermissive]
         int t=__gcd(a,b),__gcd(a,b);
                                   ^