View Compilation Error

0_0_9100672_11951.cpp: In function `void dfs(int, int, int, int)':
0_0_9100672_11951.cpp:15: error: `flag' undeclared (first use this function)
0_0_9100672_11951.cpp:15: error: (Each undeclared identifier is reported only once for each function it appears in.)
0_0_9100672_11951.cpp:37: error: void value not ignored as it ought to be
0_0_9100672_11951.cpp:38: error: return-statement with a value, in function returning 'void'
0_0_9100672_11951.cpp: In function `int main()':
0_0_9100672_11951.cpp:65: error: void value not ignored as it ought to be