Compilare: main.cpp: In function 'int main()': main.cpp:24:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < expression.size(); ++i) { ~~^~~~~~~~~~~~~~~~~~~ main.cpp:44:71: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (expression[i + 1] == '+' || expression[i + 1] == '-' || i == expression.size() - 1) { ~~^~~~~~~~~~~~~~~~~~~~~~~~ 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.in", "r", stdin); ^ main.cpp:10:36: 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); ^