Compilare: user.cpp: In function ‘int main()’: user.cpp:19:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<s1.length();i++) ^ user.cpp:21:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=1;i<s2.length();i++) ^ user.cpp:27:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if(nreq==s2.length()) { ^