c++：完成下列两道c++题

第一题的代码如下：

#include <iostream>

void main()
{
	int a;
	int sum = 0,i,j;
	while(true)
	{
		cout <<"请输入一个数：";
		cin >> a;
		if (a < 0)
		{
			cout << a  << "<0，不满足要求.";
		}else
		{
			sum = 0.0;
			for (i = 1; i <=a; i++)
			{
				if(i%3 == 0)
					sum += i;
			}
			cout<< "结果=" << sum << endl;
		}
	}
	
	
}

第二题的代码如下：

#include <iostream>
#include <string>
using namespace std;
void fun()
{
	int i;
	string buf;
	while(true)
	{
		cout <<"请输入字符：";
		getline(cin,buf);  //读取一行字符
		for (i = 0; i < buf.length();i++)
		{
			if(buf[i] >= 'a' && buf[i] <= 'z')
			{
				//do nothint
				
			}else if (buf[i] >= 'A' && buf[i] <= 'Z')
			{
				cout <<"输入的字符含有大写字母。";
				break;
			}else if (buf[i] >= '0' && buf[i] <= '9')
			{
				cout <<"输入的字符含有数字。";
				break;
			}else if (buf[i] <= 31 || buf[i] == 127)
			{
				cout <<"输入的字符中含有控制字符。";
				break;
			}else
			{
				cout <<"输入的字符非字母。";
				break;
			}
		}
		if (i == buf.length())
		{
			cout << "输入的字符全是小写字母" << endl;
		}
	}
}
void main()
{
	fun();	
}