4.21 4.22

4.21

#include <iostream>
#include <string>
#include <cctype>
#include <vector>
using namespace std;

int main()
{
	vector<int> ivec = { 1,2,3,4,5,6,7,8,9 };

	for (auto iter = ivec.begin(); iter != ivec.end(); ++iter)
	{
		*iter = (*iter) % 2 ? *iter * 2 : *iter;
	}

	return 0;

}              

4.22

#include <iostream>
#include <string>
#include <cctype>
#include <vector>
using namespace std;

int main()
{
	cout << "Enter a number:";
	int grade;
	while(cin >> grade)
	{
		string finalgrade;
		finalgrade = (grade>100||grade<0)?"wrong number":(grade > 90) ? "high pass" : (grade > 75) ? "pass" : (grade >= 60) ? "low pass" : "fail";
		cout << grade << ":" << finalgrade << endl;
	};
	return 0;

}                

if 版本

#include <iostream>
#include <string>
#include <cctype>
#include <vector>
using namespace std;

int main()
{
	cout << "Enter a number:";
	int grade;
	while(cin >> grade)
	{
		string finalgrade;
		if (grade > 100 || grade < 0)
			cout << grade << grade<<": wrong number"<<endl;
		else if (grade > 90)
			cout << grade << ": high pass"<<endl;
		else if (grade > 75)
			cout << grade << ": pass"<<endl;
		else if (grade >= 60)
			cout <<grade<< ": low pass"<<endl;
		else cout << grade << ": fail"<<endl;
		
	};
	return 0;

}                   

if版本虽然较为清晰，但是相对繁琐，条件格式虽然简洁，但是可读性少差