根据以下函数关系,对输入的不同的x值,计算出相应的y值.
0 x＜0
y= x 0≤x＜10
10 10≤x＜20
-0.5x+20 20≤x＜40
# include "stdio.h"
void main( )
{ int x,c;
float y;
scanf("%d",&x);
if (________) c=-1;
else c=__________;
switch (c)
{ case -1:y=0; break;
case 0:y=x; break;
case 1:y=10; break;
case 2:
case 3:y=-0.5*x+20; break;
default:y=-2;
}
if (_______) printf("y=%f\n",y);
else printf("error\n");
}