Compilare: main.cpp: In function 'int main()': main.cpp:15:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int j = 0; j < s.size() == 0 ? N : s.size(); j++) s3 += c; ~~^~~~~~~~~~ main.cpp:15:31: warning: suggest parentheses around comparison in operand of '==' [-Wparentheses] main.cpp:26:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (x == s.size()) i--; ~~^~~~~~~~~~~