#include<stdio.h>
int main()
{
    double x,y;
    printf("请输入X的值\n");
    scanf("%f",&x);   
    if(x<10)
    {   
        if(x<1)
            printf("%f\n",x);
        else   
            y=2*x-1;
            printf("%f\n",y);
    }
        else
        y=3*x-11;
        printf("%f\n",y);
    return 0;
}

        else
        y=3*x-11;
        printf("%f\n",y);

怎么不打括号了

#include<stdio.h>
 int main()
 {
     double x,y;
     printf("请输入X的值\n");
     scanf("%lf",&x);   
    if(x<10)
     {   
        if(x<1)
             printf("%lf\n",x);
         else   
            y=2*x-1;
             printf("%lf\n",y);
     }
         else
         y=3*x-11;
      printf("%lf\n",y);
      return 0;
 }

楼主，语意不明呀？！

if else就行了

定义双精度输入输出都用单精度低级错误

用if   else好点

支持2楼

%f与%lf的区别。多条语句打个{}。同一条if...else,上下对齐，便于检查。