# 循环小示例，菲波拉契序列，循环解一元二次方程以及switch示例程序

```# include <stdio.h>

int main(void)
{
int n;
int i;
int f1, f2, f3;

f1 = 1;
f2 = 1;

printf("请输入您需要求的想的序列：");
scanf("%d", &n);

for (i=3; i<n; i++)
{
f3 = f1 + f2;
f1 = f2;
f2 = f3;
printf("%d ", f3);
}

return 0;
}```

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

int main(void)
{
double a, b, c;
double delta;
double x1, x2;
char ch;

do {
printf("请输入一元二次方程的三个系数：\n");
printf("a = ");
scanf("%lf", &a);

printf("b = ");
scanf("%lf", &b);

printf("c = ");
scanf("%lf", &c);

delta = b*b - 4*a*c;

if (delta > 0)
{
x1 = (-b + sqrt(delta))  / (2*a);
x2 = (-b - sqrt(delta)) / (2*a);
printf("有两个解，x1 = %f, x2 = %f\n", x1, x2);
}
else if (0 == delta)
{
x1 = x2 = (-b) / (2*a);
printf("有唯一解，x1 = x2 = %f\n", x1, x2);
}
else
{
printf("无实数解！");
}

printf("您想继续么(Y/N)：");
scanf(" %c", &ch);	//%c前面必须得加一个空格 原因略，这是一个空白符的问题

} while ('y'==ch || 'Y'==ch);

return 0;
}```

switch 示例：

```# include <stdio.h>

int main(void)
{
int val;

printf("请输入您要进入的楼层：");
scanf("%d", &val);

switch (val)
{
case 1:
printf("1层开！\n");
break;
case 2:
printf("2层开！\n");
break;
case 3:
printf("3层开！\n");
break;
default:
printf("还没盖到这一层！\n");
break;
}

return 0;
}```

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