View Compilation Error

0_0_6390776_30858.cpp: In function `int bfs(node)':
0_0_6390776_30858.cpp:36: error: `flag' undeclared (first use this function)
0_0_6390776_30858.cpp:36: error: (Each undeclared identifier is reported only once for each function it appears in.)
0_0_6390776_30858.cpp: In function `int main()':
0_0_6390776_30858.cpp:110: error: `flag' undeclared (first use this function)