View Compilation Error

0_0_33084177_23502.cpp: In function 'bool spfa()':
0_0_33084177_23502.cpp:47:2: error: 'stack' was not declared in this scope
  stack<int> q;
  ^
0_0_33084177_23502.cpp:47:8: error: expected primary-expression before 'int'
  stack<int> q;
        ^
0_0_33084177_23502.cpp:49:2: error: 'q' was not declared in this scope
  q.push(1);
  ^