Compilare: main.cpp: In function 'int main()': main.cpp:16:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < s1.size(); ++i) { ~~^~~~~~~~~~~ main.cpp:26:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < s1.size(); ++i) { ~~^~~~~~~~~~~ main.cpp:37:29: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = s1.size(); i < s2.size(); ++i) { ~~^~~~~~~~~~~