Compilare: user.cpp: In function ‘int main()’: user.cpp:20:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (i=0;i<s.size();i++) if (!frecv[j][s[i]-'a']) {frecv[j][s[i]-'a']=i+1; s[i]=(nr++) + 'a';} ^ user.cpp:30:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (i=0;i<s.size();i++) if (!frecv[j+maxn][s[i]-'a']) {frecv[j+maxn][s[i]-'a']=i+1; s[i]=(nr++) + 'a';} ^