info.hpp:

#ifndef INFO_HPP
#define INFO_HPP

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

class Info{
	public:
		Info(string a,string b,string c,int d) : nickname(a),contact(b),city(c),n(d){}
		void print(){
			cout << "称呼：    " << nickname << endl;
			cout << "联系方式：" << contact << endl;
			cout << "所在城市：" << city << endl;
			cout << "预定人数：" << n << endl;
		}
	private:
	    string nickname;
		string contact;
		string city;
		int n;	
	
};

#endif

task5.cpp：

#include"info.hpp"
#include<iostream>
#include<string>
#include<vector>

int main()
{
	vector<Info> audience_info_list;
	const int capacity = 100;
	string _nickname,_contact,_city;
	int count = 0,num;
	char a;
	
	
	cout << "录入信息：" << endl;
	cout << endl;
	cout << "称呼/昵称， 联系方式（邮箱/手机号）， 所在城市， 预定参加人数" << endl;
	
	while( cin >> _nickname){
  		cin >> _contact;
		cin >> _city;
		cin >> num;
		
	    if( num + count > capacity)	{
	    	cout << "对不起，只剩" << capacity - count << "个位置。" << endl;
	    	cout << "1. 输入u，更新（update）预定信息" << endl;
	    	cout << "2. 输入q，退出预定" << endl;
	    	cout << "你的选择：";
	    	cin >> a;
	    	if(a == 'q'){
	    		break;
			}else{
				cout << "请重新输入：" << endl;
				continue;
			}
	    }
	    
	    count += num;
	    audience_info_list.push_back(Info(_nickname,_contact,_city,num));
	    
	}
	
	cout << "目前一共有" << count << "位听众预定参加，预定听众信息如下：" << endl;
	for ( int i = 0;i < audience_info_list.size();i++){
		audience_info_list[i].print();
	}
	   	
}

　运行结果：

textcoder.hpp:

#ifndef TEXTCODER_HPP
#define TEXTCODER_HPP

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

class TextCoder{
	public:
		TextCoder(string x):text(x){}
		
		string encoder(){
			string str = text;
			for(int i = 0;i < text.length();i++){
				
				if(text[i] >= 'a' && text[i] <= 'z'){
					str[i] = (text[i] + 5 - 'a') % 26 + 'a';
				}else if(text[i] >= 'A' && text[i] <= 'Z'){
					str[i] = (text[i] + 5 - 'A') % 26 + 'A';
				}
				
			} 
			return str;
		}	
				
		string decoder(){
			string str = text;
			for(int i = 0;i < text.length();i++){
				
				if(text[i] >= 'a' && text[i] <= 'z'){
					str[i] = (text[i] - 5 - 'a' + 26) % 26 + 'a';
				}else if(text[i] >= 'A' && text[i] <= 'Z'){
					str[i] = (text[i] - 5 - 'A' + 26) % 26 + 'A';
				}
				
			}
			return str;
		}
		
	private:
	    string text;	
};
#endif

task6.cpp:

#include "TextCoder.hpp"
#include<iostream>
#include<string>
int main()
{
    string text, encoded_text, decoded_text;
    
    cout << "输入英文文本: ";
    
    while (getline(cin, text))
    {
        
        encoded_text = TextCoder(text).encoder();  // 这里使用的是临时无名对象
        cout << "加密后英文文本:\t" << encoded_text << endl;

        decoded_text = TextCoder(encoded_text).decoder(); // 这里使用的是临时无名对象
        cout << "解密后英文文本:\t" << decoded_text << endl;
        cout << "\n输入英文文本: ";
    }
}

运行结果：