Compilare: user.cpp: In function ‘int eval()’: user.cpp:20:24: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if(ind<strlen(s) && s[ind]==')') ^ user.cpp:25:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while(ind<strlen(s) && s[ind]>='0' && s[ind]<='9'){ ^ user.cpp: In function ‘int main()’: user.cpp:79:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while(ind<strlen(s)) ^ user.cpp:75:26: warning: ignoring return value of ‘char* fgets(char*, int, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] fgets(s, 100000, fin); ^