View Compilation Error

638440_0_0_24336.cpp: In function `void bfs(int)':
638440_0_0_24336.cpp:30: error: `flag' undeclared (first use this function)
638440_0_0_24336.cpp:30: error: (Each undeclared identifier is reported only once for each function it appears in.)
638440_0_0_24336.cpp: In function `void slove()':
638440_0_0_24336.cpp:40: error: `flag' undeclared (first use this function)