Compilare: user.cpp: In function ‘int main()’: user.cpp:59:42: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if(first && first<S.size() && last && last<S.size()&& S[first]==S[last] && S[first]==-sum)sol+=(last-first+1); ^ user.cpp:59:67: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if(first && first<S.size() && last && last<S.size()&& S[first]==S[last] && S[first]==-sum)sol+=(last-first+1); ^ user.cpp:60:49: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] else if((first && first<S.size() && S[first] == -sum) ^ user.cpp:61:45: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] || (last && last<S.size() && S[last] == -sum)) ^