Compilare: main.cpp: In function 'int ecuation_solver(std::__cxx11::string, std::vector<int>)': main.cpp:85:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<formula.length();++i){ ~^~~~~~~~~~~~~~~~~ main.cpp:92:52: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while(is_digit(formula[index]) && index<formula.length()){ ~~~~~^~~~~~~~~~~~~~~~~ main.cpp:103:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<signs.size();++i){ ~^~~~~~~~~~~~~ main.cpp:112:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<signs.size();++i){ ~^~~~~~~~~~~~~ main.cpp: In function 'int function_solver(std::__cxx11::string, std::__cxx11::string)': main.cpp:134:54: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while(is_digit(variables[ind]) && ind<variables.length()){ ~~~^~~~~~~~~~~~~~~~~~~ main.cpp: In function 'int main()': main.cpp:194:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int j=1;j<v.size();++j){ ~^~~~~~~~~