4.4 循环案例选讲（阶乘、质数）

左手的ㄟ右手 2022-05-20 05:48 42阅读 0赞

![70][]![70 1][]![70 2][]

#include<iostream>
    #include<cstdio>
    using namespace std;
    int main()
    {
    	int a, n, q = 1;
    	cin >> a >> n;
    	for(int i = 1; i <= n; ++i)
    	{
    		q *= a;
    	}
    	cout << q << endl;
    	return 0;
    }

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【分析】这里输入有负数，设最大值为maxn，此时maxn的初始值不能再设置为0了，可以设置第一个数为最大值，然后用其他的数与它比较，慢慢更新最大值。

#include<iostream>
    #include<cstdio>
    using namespace std;
    int main()
    {
    	int n, maxn;
    	cin >> maxn;//假设输入的第一个数就是最大值 
    	while(cin >> n)
    	{
    		if(n > maxn) //比较更新最大值 
    			maxn = n;
    	}
    	cout << maxn << endl;
    	return 0;
    }

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#include<iostream>
    #include<cstdio>
    using namespace std;
    int main()
    {
    	 int n, max1, max2;
    	 int num = 0;
    	 while (cin >> n)
    	 {
    	 	++num;
    	 	if (num == 1)//假设初始值最大 
    	 	{
    	 		max1 = n;
    		}
    		else if(num == 2)//两个数的情况 
    		{
    			if(n > max1)
    			{
    				max2 = max1;
    				max1 = n;				
    			}
    			else
    				max2 = n;
    		}
    		else //3个及其以上数的情况 
    		{
    			if(n >= max1)
    			{
    				max2 = max1;
    				max1 = n;				
    			}
    			else if(n > max2)
    			{
    				max2 = n;
    			}
    		}
    	 }
    	 cout << max1 << " " << max2 << endl;
    	 return 0;
    }

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#include<iostream>
    #include<cstdio>
    using namespace std;
    int main()
    {
    	int n, f1, f2, f3;
    	cin >> n;
    	f1 = 1, f2 = 1;
    	if(n == 1 || n == 2)
    		cout << "1" << endl;
    	else
    	{
    		for(int i = 3; i <= n; ++i)
    		{
    			f3 = f1 + f2;
    			f1 = f2;
    			f2 = f3;
    		}
    		cout << f3 << endl;
    	}
    	return 0;
    }

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#include<iostream>
    #include<cstdio>
    using namespace std;
    int main()
    {
    	int n, sum = 0, q = 1;
    	cin >> n;
    	for(int i=1; i<=n; ++i)
    	{
    		q *= i;
    		sum += q;
    	} 
    	cout << sum << endl;
    	return 0;
    }

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一个数，如果只有1和它本身两个 [因数][Link 1] ，这样的数叫质数（或素数）。如2、3、5、7都是质数。   
一个数，如果除了1和它本身还有别的因数，这样的数叫 [合数][Link 2] 。如4、6、15、49都是合数。   
1既不是质数，也不是合数。

#include<iostream>
    #include<cstdio>
    using namespace std;
    int main()
    {
    	int n;
    	cin >> n;
    	cout << 2 << endl;
    	for(int i = 3; i <= n; i += 2)//i += 2删除偶数的情况 
    	{
    		int j;
    		for(j = 3; j < i; j += 2)//j += 2 奇数的因子不可能为偶数，为奇数 
    		{
    			if(i % j == 0) break;
    			if(j * j > i) break;//j大于i的平方根后，另一个因子肯定小于i的平方根，已经计算过了	
    		}
    		if(j * j > i) 
    			cout << i << endl;
    	}
    	return 0;
    }

#include<iostream>
    #include<cstdio>
    #include<cmath>
    using namespace std;
    int main()
    {
    	int n;
    	cin >> n;
    	cout << 2 << endl;
    	for(int i = 3; i <= n; i += 2)//i += 2删除偶数的情况 
    	{
    		int j;
    		for(j = 3; j < sqrt(i); j += 2)//j += 2 奇数的因子不可能为偶数，为奇数 
    		{
    			if(i % j == 0) break;
    		}
    		if(j > sqrt(i))
    			cout << i << endl;
    	}
    	return 0;
    }

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[Link 1]: http://www.so.com/s?q=%E5%9B%A0%E6%95%B0&ie=utf-8&src=internal_wenda_recommend_textn
[Link 2]: http://www.so.com/s?q=%E5%90%88%E6%95%B0&ie=utf-8&src=internal_wenda_recommend_textn