输入X 计算并输出y值 公式为 y= 0 x

#include
int main(void)
{
double x;
scanf("%lf",&x);
if(x < 0.0)
{
printf("y = 0\n");
}
else if(x >= 0.0 && x < 10.0)
{
printf("y = %lf\n",x);
}
else if(x >= 10.0 && x < 20.0)
{
printf("y = 10\n");
}
else if(x >= 20.0 && x < 40.0)
{
printf("y = %lf\n",-x/2+20.0);
}
}