0_0_17835110_30571.cpp: In function 'llt kmul(llt, llt)': 0_0_17835110_30571.cpp:28:17: error: invalid operands of types 'llt [20] {aka long long int [20]}' and 'llt [20] {aka long long int [20]}' to binary 'operator+' a = a + a; ^