#include<stdio.h>
#include<malloc.h>
union nuionnum
{
double num1;
char num2;
};
struct lianbiao
{
struct lianbiao *p;
union nuionnum num;
int flage;/* 标志数字符号 */
};

void main()
{
 char c;
 struct lianbiao lianhe;
 struct lianbiao *next;
 printf("请输入计算机能识别四则运算表达式:a+b*(c+d)/e\n");
 while(1)
 {
  first:
  next=&lianhe;
  while((int)(c=getchar())!=10)
  {
   loop:
   /* 表达式放入复合链表 */
   if (c=='+'||c=='-'||c=='*'||c=='/'||c=='('||c==')')
   {
     next->num.num2=c;
     if (c== '+' || c== '-' )
      next->flage =1;
     else if(c== '*' ||c== '/' )
      next->flage =2;
     else if(c== '(' )
      next->flage =3;
     else if(c== ')' )
      next->flage =4;
     next->p=calloc(1,sizeof(struct lianbiao));
     next=next->p;
     next->p=NULL;
   }
   else if(c>='0'&&c<='9')
   { long int t=1;
     int flag=0;
     next->num.num1=c-48;
     while(((c=getchar())>='0'&&c<='9')||c=='.')
     {
       if (flag==1 && c!='.')
       {
         t=t*10;
         next->num.num1=next->num.num1+(c-48.0)/t;
       }
       else if(c>='0'&&c<='9')
        next->num.num1=next->num.num1*10+c-48;
       if (c=='.')
       {
         flag=1;
       }
     }
     next->flage =0;
     next->p=calloc(1,sizeof(struct lianbiao));
     next=next->p;
     next->p=NULL;
     if (c=='\n')break;
     goto loop;
   }
   else
   {
     printf("不是合法算术表达式!!!\n请重新输入:\n");
     while(getchar()!='\n') ;/* 设置重新输入 */
     goto first;
   }
  }
  /* 链表数字符号别入栈 */
  next=&lianhe;
  {
    int i=0,j=0;/* 用标记栈顶点 */
    double arrd[100];
    char arrc[2][100];
    while(next->p!=NULL)
    {
      if (next->flage !=0&&next->num.num2==')')/* 括号外理 */
      {
        while(arrc[0][i-1]!='(')/* 栈 */
        {
          if (arrc[0][i-1]=='+')
          {
            arrd[j-2]=arrd[j-2]+arrd[j-1];
            i=i-1;
            j=j-1;
          }
          else if(arrc[0][i-1]=='-')
          {
            arrd[j-2]=arrd[j-2]-arrd[j-1];
            i=i-1;
            j=j-1;
          }
          else if(arrc[0][i-1]=='*')
          {
            arrd[j-2]=arrd[j-2]*arrd[j-1];
            i=i-1;
            j=j-1;
          }
          else if(arrc[0][i-1]=='/')
          {
            arrd[j-2]=arrd[j-2]/arrd[j-1];
            i=i-1;
            j=j-1;
          }
        }
        i=i-1;
      }
      else if (next->num.num2 =='(')/* 入栈 */
      {
        arrc[1][i]=next->flage;
        arrc[0][i]=next->num.num2;
        i++;
      }
      else if (next->flage !=0)/* 运算复符理 */
      {
       front:
        if (i>0&&next->flage<arrc[1][i-1]&&arrc[1][i-1]!=3)
        {
          if (arrc[0][i-1]=='*')
          {
            arrd[j-2]=arrd[j-2]*arrd[j-1];
            i=i-1;
            j=j-1;
          }
          else if(arrc[0][i-1]=='/')
          {
            arrd[j-2]=arrd[j-2]/arrd[j-1];
            i=i-1;
            j=j-1;
          }
          goto front;
        }
        arrc[1][i]=next->flage;
        arrc[0][i]=next->num.num2;
        i++;
      }
      else
      {
        arrd[j]=next->num.num1; /* 数字理 */
        j++;
      }
      next=next->p;
    }
    while(i!=0)/* 全部入栈椎外理 */
    {
      if (arrc[0][i-1]=='+')
      {
        arrd[j-2]=arrd[j-2]+arrd[j-1];
        i=i-1;
        j=j-1;
      }
      else if (arrc[0][i-1]=='-')
      {
        arrd[j-2]=arrd[j-2]-arrd[j-1];
        i=i-1;
        j=j-1;
      }
      else if (arrc[0][i-1]=='*')
      {
        arrd[j-2]=arrd[j-2]*arrd[j-1];
        i=i-1;
        j=j-1;
      }
      else if(arrc[0][i-1]=='/')
      {
        arrd[j-2]=arrd[j-2]/arrd[j-1];/* 1+2*3/4+5  5   ++ 1 1.5  */
        i=i-1;
        j=j-1;
      }
    }
    printf("%lf\n",arrd[0]);
  }
 }
}
==============================end=============================
为什么老提示“不是合法的算术表达式”，要重新输入呢？？？