View Compilation Error

0_0_29979457_29018.cpp: In function 'long long int multi(long long int, long long int, long long int)':
0_0_29979457_29018.cpp:7:9: error: expected identifier before '(' token
  return (__int128)x * y % mod;
         ^
0_0_29979457_29018.cpp:7:2: error: named return values are no longer supported
  return (__int128)x * y % mod;
  ^
0_0_29979457_29018.cpp:19:33: error: 'n' was not declared in this scope
   if (y & 1)res = multi(res, x, n);
                                 ^
0_0_29979457_29018.cpp:21:19: error: 'n' was not declared in this scope
   x = multi(x, x, n);
                   ^
0_0_29979457_29018.cpp: In function 'bool miller_rabin(long long int)':
0_0_29979457_29018.cpp:44:23: error: 'mypow' was not declared in this scope
   ll b = mypow(a, t, n);
                       ^
0_0_29979457_29018.cpp: In function 'int main()':
0_0_29979457_29018.cpp:63:40: error: 'mypow' was not declared in this scope
    ans = multi(ans, mypow(now, P - 2, P), P);
                                        ^