C++考查课试题，急用，谢谢

题目1：

#include <iostream>
using namespace std;
int main()
{
	int i,n,sum = 0;;
	cout << "请输入n:";
	cin >> n;
	for ( i = 1;i <=n; i++)
	{
		sum += i;
	}
	cout << " 1 + 2 + ...+ " << n << " = " << sum;
	return 0;
}

题目2：

#include <iostream>
#include <string>
using namespace std;
int main()
{
	int zm = 0,nmb = 0;
	string ss;
	cout << "请输入字符串:";
	cin >> ss;
	for (int i = 0; i < ss.length(); i++)
	{
		if (ss.at(i) >= '0' && ss.at(i) <= '9')
		{
			nmb++;
		}else if (ss.at(i) >= 'a' && ss.at(i) <= 'z' || ss.at(i) >= 'A' && ss.at(i) <= 'Z')
		{
			zm++;
		}
	}
	cout << "字母字符:" << zm << ";数字字符:" <<nmb;
	return 0;
}

题目3：

#include <iostream>
using namespace std;

double fun(int n)
{
	int i;
	int* a = new int[n];
	int* b = new int[n];
	a[0] = 1;
	a[1] = 2;
	b[0] = 2;
	b[1] = 3;
	double sum = b[0]/a[0] + b[1]/b[1];
	for (i = 2; i < n; i++)
	{
		a[i] = a[i-1] + a[i-2];
		b[i] = b[i-1] + b[i-2];
		sum += 1.0 * b[i]/a[i];
	}
	return sum;
}
int main()
{
	int n;;
	cout << "请输入n:";
	cin >> n;
	
	cout << "前" << n << "项的和 = " << fun(n);
	return 0;
}

题目4：

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

int main()
{
	float x,y;
	
	cout << "请输入x和y:";
	cin >> x >> y;
	float fu;
	if (x >= 0)
	{
		fu = 2 * x + y * y;
	}else
		fu = 2 * x + y;

	cout << "值:" << setiosflags(ios::fixed)<<setprecision(2)<< fu <<endl;
	return 0;
}

题目5：

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

bool issxh(int n)
{
	int dd = n;
	int a = n%10;
	n = n/10;
	int b = n%10;
	n=n/10;
	int c = n%10;
	int ss = a*a*a + b*b*b + c*c*c;
	if (ss == dd)
	{
		return true;
	}
	return false;

}

int main()
{
	for (int i = 100; i < 999; i++)
	{
		if(issxh(i))
			cout << i << " ";
	}

	cout << endl;
	return 0;
}

题目6：

#include <iostream>
#include <string>
using namespace std;
int prime(int n)
{
	int i =2;
	for(i = 2; i<n; i++)
		if(n%i == 0)
			return 0;
	return 1;
}

int main()
{
	int a[20]={0};
	int b[20] = {0};
	int nmb = 0;
	cout << "请输入20个正整数:";
	for (int i = 0; i < 20; i++)
	{
		cin >> a[i];
		if(prime(a[i]))
			b[nmb++] = a[i];
	}
	
	for (int i=0; i < nmb-1; i++)
	{
		for (int j = 0; j < nmb -1-i;j++)
		{
			if (b[j] < b[j+1])
			{
				int tt = b[j];
				b[j] = b[j+1];
				b[j+1] = tt;
			}
		}
	}
	cout << "所有素数降序输出:"<< endl;
	for(int i = 0; i < nmb;i++)
		cout << b[i] << " ";
	cout << endl;
	return 0;
}

都是基础题，题主不妨先写，有问题在探讨

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