program1.cpp: In function 'void dfs(int)': program1.cpp:9: warning: comparison between signed and unsigned integer expressions program1.cpp: In function 'int main()': program1.cpp:30: warning: NULL used in arithmetic program1.cpp:14: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result program1.cpp:15: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result program1.cpp:17: warning: ignoring return value of 'char* gets(char*)', declared with attribute warn_unused_result program1.cpp:42: warning: ignoring return value of 'char* gets(char*)', declared with attribute warn_unused_result /tmp/ccDUUkXS.o: In function `main': program1.cpp:(.text+0x156): warning: the `gets' function is dangerous and should not be used.