Compilare: main.cpp: In function 'int main()': main.cpp:18:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i <= str.size() && flag; ++i) if (i == str.size() || str[i] != ch) { ~~^~~~~~~~~~~~~ main.cpp:18:55: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i <= str.size() && flag; ++i) if (i == str.size() || str[i] != ch) { ~~^~~~~~~~~~~~~ main.cpp:19:10: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (i == str.size()) ~~^~~~~~~~~~~~~ main.cpp:25:10: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (i < str.size()) ~~^~~~~~~~~~~~