#include <stdio.h>
#include <stdlib.h>
struct tax
{
      float taxrate;
      float beforetax;
      float lowline;
}taxx[100];
struct tax taxx[1]={0,0,0};
struct tax taxx[2]={0.05,0,1600};
struct tax taxx[3]={0.1,25,2100};
struct tax taxx[4]={0.15,175,3600};
struct tax taxx[5]={0.2,625,6600};
struct tax taxx[6]={0.25,3625,21600};
struct tax taxx[7]={0.3,8625,41600};
struct tax taxx[8]={0.35,14625,61600};
struct tax taxx[9]={0.4,21625,81600};
struct tax taxx[10]={0.45,29625,101600};            //分别为十档的对应税率与其上一档总税金
float tax(float a,float b,float c) //a为上一档总税金,b此档应缴税部分，c为此档税率
{
      float y;
      y=a+b*c;
      return y;
}
main()
{
      float x,y,a,b;
      int i;
      do
      {
            printf("please input income amount(more than zero)\n");
            scanf("%f",&x);
      }while(x<=0);
      if(x>=1||x<=1600)
      {
      i=1;
      }
      elseif(x>=1601||x<=2100)
      {
      i=2;
      }
      elseif(x>=2101||<=3600)
      {
      i=3;
      }
      elseif(x>=3601||x<=6600)
      {
      i=4;
      }
      elseif(x>=6601||<=21600)
      {
      i=5;
      }
      elseif(x>=21601||x<=41600)
      {
      i=6;
      }
      elseif(x>=41601||x<=61600)
      {
      i=7;
      }
      elseif(x>=61601||x<=81600)
      {
      i=8;
      }
      elseif(x>=81601||x<=101600)
      {
      i=9;
      }
      elseif(x>=101600)
      {
      i=10;
      }
      a=taxx[i].beforetax;
      b=taxx[i].taxrate;
      c=x-taxx[i].lowline;
      y=tax(a,c,b);
      printf("your income is %f\nyou should pay %f for tax.\n",x,y);
      system("pause");
}

struct tax taxx[1]={0,0,0}; 有错误，报错：conflicting types for 'taxx'
为什么？

taxx[1].taxrate = 0;
taxx[1].beforetax = 0;
taxx[1].lowline = 0;
把你main函数外面的这些taxx之类的赋值操作都以上面的方式放在main函数里面赋值，你这种赋值方式只适合于声明的时候赋初值，你定义结构体时就声明了，但是没有赋初值，就不能这样用了。

我也是新手- -！不过你比我学的多多啦，互相勉励啦，顶了！！

你的数组貌似没有定义啊!就是taxx[100];
 struct tax taxx[1]={0,0,0};
 struct tax taxx[2]={0.05,0,1600};
 struct tax taxx[3]={0.1,25,2100};
 struct tax taxx[4]={0.15,175,3600};
 struct tax taxx[5]={0.2,625,6600};
 struct tax taxx[6]={0.25,3625,21600};
 struct tax taxx[7]={0.3,8625,41600};
 struct tax taxx[8]={0.35,14625,61600};
 struct tax taxx[9]={0.4,21625,81600};
 struct tax taxx[10]={0.45,29625,101600};
没有定义定义什么类型。

直接定义数组struct tax taxx[9]={{0,0,0},{},{},,,{}};