Main.cc: In function 'int main()': Main.cc:7:21: warning: comparison with string literal results in unspecified behaviour [-Waddress] while(a[len_a]!="/0"){ ^ Main.cc:7:21: error: ISO C++ forbids comparison between pointer and integer [-fpermissive] Main.cc:10:21: warning: comparison with string literal results in unspecified behaviour [-Waddress] while(a[len_b]!="/0"){ ^ Main.cc:10:21: error: ISO C++ forbids comparison between pointer and integer [-fpermissive]