c++primer:string.size()

注意string.size()的返回类型在大多数时候都是一个无符号的值,在vs2010上实验是usinged int,如果拿来做运算会自动将int转换成unsinged int

string s ;
cin>>s;
int n = -1;
bool test =  (int(s.size())<n);
cin>>s;
int n = -1;
bool test =  (s.size()<n);