运行结果为啥和书上不一样

/ex3_6.c/
#include
void main(){
double x,y;
printf("Enter x:");
scanf("%1f",&x);
if(x<0);
y=0;
else if(x<=15)
y=4x/3;
else
y=2.5x-10.5;
printf("f(%.2f)=%.2f\n",x,y);
}

scanf("%1f",&x);
改为
scanf("%lf",&x);
if(x<0);尾部的分号删掉

语法错误了，if后边分号去掉