Compilare: user.cpp: In function ‘int fact()’: user.cpp:19:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (i < s.length() && s[i] == '(') { ^ user.cpp:24:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while (i < s.length() && s[i] >= '0' && s[i] <= '9') { ^ user.cpp: In function ‘int term()’: user.cpp:34:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while (i < s.length() && (s[i] == '*' || s[i] == '/')) { ^ user.cpp: In function ‘int exp()’: user.cpp:48:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while (i < s.length() && (s[i] == '+' || s[i] == '-')) { ^