Compilare: main.cpp: In function 'int main()': main.cpp:23:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < expression.size(); ++i) { ~~^~~~~~~~~~~~~~~~~~~ main.cpp:43:66: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (expression[i+1] == '+' || expression[i+1] == '-' || i==expression.size()-1) { ~^~~~~~~~~~~~~~~~~~~~~ main.cpp:8:32: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen("eq4.in","r",stdin); ^ main.cpp:9:34: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen("eq4.out","w",stdout); ^