第四章 4.7 条件运算符

4.21 编写一段程序，使用条件运算符从vector< int > 中找到哪些元素的值是奇数，然后将这些奇数的值翻倍。

#include <iostream>#include <vector>using namespace std;int main(){    vector<int> vint{ 1, 2, 3, 4, 5, 6, 7, 8, 9, 0 };    for (auto &iter = vint.begin(); iter != vint.end(); ++iter)    {        bool result = *iter % 2 == 0 ? false : true;        if (result)        {            *iter = *iter * 2;        }        cout << *iter << " ";    }    return 0;}

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4.22

#include <iostream>#include <string>using namespace std;int main(){    int grade = 78;    string finalgrade = (grade > 90) ? "high pass" : (grade > 75) ? "low pass" : (grade < 60) ? "fail" : "pass";    cout << finalgrade << endl;    if (grade > 90)    {        finalgrade = "high pass";    }    else if (grade > 75)    {        finalgrade = "low pass";    }    else if (grade < 60)    {        finalgrade = "fail";    }    else    {        finalgrade = "pass";    }    cout << finalgrade << endl;    return 0;}

ifelse更容易理解，条件运算符更简洁。

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4.23修改语句

string s = "word";string p1 = s + s[s.size() - 1] == 's' ? "" : "s";//err +优先级高于== string p1 = s + (s[s.size() - 1] == 's' ? "" : "s");//p1 = “words”

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4.24本节的示例程序是将成绩划分成high pass、pass和fail三种，它的依据是条件运算符满足右结合律。假如条件运算符满足的是左结合律，求值过程是怎样的？
先判断grade < 60，false再判断grade > 90;