concat.cpp: In function `int valid(int)': concat.cpp:13: warning: comparison between signed and unsigned integer expressions concat.cpp:7: warning: unused variable `long int j' concat.cpp:7: warning: unused variable `long int u' concat.cpp: In function `int strmatei(char*, char*)': concat.cpp:26: warning: comparison between signed and unsigned integer expressions concat.cpp: In function `void back(int)': concat.cpp:38: warning: unused variable `long int j' /tmp/ccbBbH2f.o(.text+0x216): In function `main': : the `gets' function is dangerous and should not be used.