Compilare: main.cpp: In function 'int main()': main.cpp:55:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < Ecuatie.size(); ++i) { ~~^~~~~~~~~~~~~~~~ main.cpp:146:17: warning: ignoring return value of 'int system(const char*)', declared with attribute warn_unused_result [-Wunused-result] system("PAUSE"); ^ main.cpp:128:2: warning: 'op' may be used uninitialized in this function [-Wmaybe-uninitialized] if (op == MINUS) { ^~