View Compilation Error

0_0_28937673_20813.cpp: In function 'int main()':
0_0_28937673_20813.cpp:14:5: error: 'thread' was not declared in this scope
     thread wa(hello,a);
     ^
0_0_28937673_20813.cpp:15:2: error: 'wa' was not declared in this scope
  wa.join();
  ^