sl.cpp: In function 'int main()': sl.cpp:36: warning: operation on 'k' may be undefined sl.cpp:36: warning: operation on 'k' may be undefined sl.cpp:39: warning: operation on 'k' may be undefined sl.cpp:39: warning: operation on 'k' may be undefined sl.cpp:17: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result sl.cpp:18: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result sl.cpp:20: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result sl.cpp:22: warning: ignoring return value of 'char* gets(char*)', declared with attribute warn_unused_result /tmp/ccnSLYY9.o: In function `main': sl.cpp:(.text+0xff): warning: the `gets' function is dangerous and should not be used.