Compilare: main.cpp: In function 'int main()': main.cpp:10:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i=1; i<a.length(); ++i){ ~^~~~~~~~~~~ main.cpp:19:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i=0; i<b.length(); ++i){ ~^~~~~~~~~~~ main.cpp:26:13: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if(j==a.length()-1){ ~^~~~~~~~~~~~~~