Compilare: main.cpp: In function 'int eval(int, int, int&)': main.cpp:33:8: warning: unused variable 'r' [-Wunused-variable] int r = 0; ^ main.cpp:56:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < op.size(); i++) { ~~^~~~~~~~~~~ main.cpp:24:6: warning: unused variable 'ln' [-Wunused-variable] int ln = -1; ^~ main.cpp: In function 'int main()': main.cpp:72:10: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while (n<str.size()) { ~^~~~~~~~~~~