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;
}