concat.cpp: In function 'int main()': concat.cpp:79: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result concat.cpp:80: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result concat.cpp:81: warning: ignoring return value of 'char* gets(char*)', declared with attribute warn_unused_result concat.cpp:83: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result concat.cpp:86: 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 concat.cpp:1: In function 'char* gets(char*)', inlined from 'int main()' at concat.cpp:86: /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/ccC70Cnt.o: In function `main': concat.cpp:(.text+0x315): warning: the `gets' function is dangerous and should not be used. concat.cpp:(.text+0x2c4): warning: the `gets' function is dangerous and should not be used.