View Compilation Error

0_0_37689134_24715.cpp: In function 'void tarjan(long long int)':
0_0_37689134_24715.cpp:29:19: error: 'in_stk' was not declared in this scope
   stk[++top] = u, in_stk[u] = true;
                   ^
0_0_37689134_24715.cpp: In function 'int main()':
0_0_37689134_24715.cpp:68:7: error: 'in_stk' was not declared in this scope
       in_stk[i] = false;
       ^