View Compilation Error

0_0_36570172_15495.cpp:2:1: error: 'mt19937_64' does not name a type
 mt19937_64 gen(time(0));
 ^
0_0_36570172_15495.cpp: In function 'int randInt(int, int)':
0_0_36570172_15495.cpp:45:13: error: 'gen' was not declared in this scope
  return gen() % (r - l + 1) + l;
             ^