C语言基础练习2

1.Fibonacci数列，兔子繁殖问题

#include <stdio.h>


int main()
{
	int f1=1, f2=1;
	int i;
	for (i = 1; i <= 20; i++)
	{
		printf("%12d %12d ", f1, f2);
		if (i % 2 == 0) printf("\n");
		f1 = f1 + f2;
		f2 = f2 + f1;
	}
    return 0;
}

2.输入一个大于3的整数n，判定是否为素数

#include <stdio.h>
#include<math.h>

int main()
{
	int n, i, k;
	printf("please enter a integer number,n=?");
	scanf_s("%d", &n);
	k = sqrt(n);
	for (i = 2; i <=k; i++)
		if (n%i == 0)break;
		if (i < k) printf("%d is not a prime number.\n", n);
		else printf("%d is a prime number.\n", n);
    return 0;
}

3.求100-200间的全部素数

#include<stdio.h>
#include<math.h>

int main()
{
	int i, k, n, m = 0;
	for (n = 101; n <= 200; n = n + 2)
	{
		k = sqrt(n);
		for (i = 2; i <= k; i++)
			if (n%i == 0)break;
		if (i >= k + 1)
		{
			printf("%d ", n);
			m = m + 1;
		}
		if (m % 10 == 0) printf("\n");
	}
	printf("\n");
    return 0;
}

4.“译密码”

#include<stdio.h>

int main()
{
	char c;
	while ((c = getchar()) != '\n')
	{
		if ((c >= 'A'&&c <= 'Z') || (c >= 'a'&&c <= 'z'))
		{
			c = c + 4;
			if (c >= 'Z'&&c <= 'Z' + 4 || c > 'z')
				c = c - 26;
		}
		printf("%c", c);
	}
	printf("\n");
    return 0;
}