Compilare: user.cpp: In function ‘int factor(int&)’: user.cpp:36:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while(ind<=s.size() && isdigit(s[ind])!=0) ^ user.cpp: In function ‘int termen(int&)’: user.cpp:46:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while(ind<=s.size() && is_op2(ind)) ^ user.cpp: In function ‘int eval(int&)’: user.cpp:59:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while(ind<=s.size() && is_op1(ind)) ^