prefix.cpp: In function 'int main()': prefix.cpp:78: warning: comparison between signed and unsigned integer expressions prefix.cpp:19: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result prefix.cpp:20: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result prefix.cpp:23: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result prefix.cpp:26: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result prefix.cpp:27: warning: ignoring return value of 'char* gets(char*)', declared with attribute warn_unused_result In file included from /usr/include/stdio.h:910, from /usr/include/c++/4.4/cstdio:45, from prefix.cpp:1: In function 'char* gets(char*)', inlined from 'int main()' at prefix.cpp:27: /usr/include/bits/stdio2.h:230: warning: call to '__gets_warn' declared with attribute warning: please use fgets or getline instead, gets can't specify buffer size /tmp/ccK3gSOq.o: In function `main': prefix.cpp:(.text+0xe5): warning: the `gets' function is dangerous and should not be used.