或不等于 [英] Or and not equal

问题描述

这为什么起作用?

#include <iostream>
#include <string>
using namespace std;
int main(){
string s="a";
if((s=="cm")||(s=="in")||(s=="ft")||(s=="m"))
        cout<<s+" Is an illegal value";
else
        cout<<"I like "+s;
        return 0;
} 

http://ideone.com/7pnYh

但是那不是

#include <iostream>
#include <string>
using namespace std;
int main(){
string s="a";
if((s!="cm")||(s!="in")||(s!="ft")||(s!="m"))
        cout<<s+" Is an illegal value";
else
        cout<<"I like "+s;
        return 0;
}  

http://ideone.com/TXUXA 我想要的答案都是我喜欢".

http://ideone.com/TXUXA The answer i want for both is "I like a" .

推荐答案

在第二种情况下， s！="cm" ，当然还有第一个 cout .要取消检查并保持逻辑不变，请执行以下操作:

In your second case s != "cm" and of course the first cout is printed. To negate the check and the logic to remain the same, do it like this:

if((s!="cm")&&(s!="in")&&(s!="ft")&&(s!="m"))
        cout<<"I like "+s;
else
        cout<<s+" Is an illegal value";

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