C语言 写的 表达式求值。

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<math.h>

#define Stack_Size 1010
#define INF 21000000
char cmp[7][8]= {">><<<>>",">><<<>>",">>>><>>",">>>><>>","<<<<<=?",">>>>?>>","<<<<<?="};
/*
>   >   <   <   <   >   >
>   >   <   <   <   >   >
>   >   >   >   <   >   >
>   >   >   >   <   >   >
<   <   <   <   <   =   ?
>   >   >   >   ?   >   >
<   <   <   <   <   ?   =
*/

typedef struct
{
char Elem[Stack_Size];
int top;
} Operator;
typedef struct
{
double Elem[Stack_Size];
int top;
} Number;
void InitStack_Operator(Operator* S)
{
S->top=-1;
}
void InitStack_Number(Number* S)
{
S->top=-1;
}
int Pop_Operator(Operator* S)
{
if(S->top==-1)
{
printf("运算符栈为空\n");
exit(10);
}
S->top--;
return 1;
}
int Pop_Number(Number* S)
{
if(S->top==-1)
{
printf("数字栈为空\n");
exit(11);
}
S->top--;
return 1;
}
int Push_Operator(Operator* S,char ch)
{
if(S->top==Stack_Size-1)
{
printf("运算符栈满\n");
exit(12);
}
S->top++;
S->Elem[S->top]=ch;
return 1;
}
int Push_Number(Number* S,double ch)
{
if(S->top==Stack_Size-1)
{
printf("运算符栈满\n");
exit(13);
}
S->top ++;
S->Elem[S->top]=ch;
return 1;
}
char Gettop_Operator(Operator *S)
{
if(S->top==-1)
{
printf("运算符栈为空\n");
exit(17);
}
return S->Elem[S->top];
}
double Gettop_Number(Number *S)
{
if(S->top==-1)
{
printf("数字栈为空\n");
exit(18);
}
return S->Elem[S->top];
}
double Calc(double a,double b,char opt)
{
double res;
if(opt=='+') res=a+b;
if(opt=='-') res=a-b;
if(opt=='*') res=a*b;
if(opt=='/')
{
if(fabs(b)<0.00000001)
{
printf("发生除0错误\n");
exit(15);
}
res=a/b;
}
//printf("%.2lf %c %.2lf = %.2lf\n",a,opt,b,res);
return res;
}
int change(char ch)
{
switch(ch)
{
case '+':
return 0;
case '-':
return 1;
case '*':
return 2;
case '/':
return 3;
case '(':
return 4;
case ')':
return 5;
case '#':
return 6;
}
return -INF;
}
char compare(char a,char b)
{
if(cmp[change(a)][change(b)]=='?')
{
printf("表达式错误\n");
exit(16);
}
return cmp[change(a)][change(b)];
}
int check(char *s,int len)
{
for(int i=0; i<len; i++)
{
if(s[i]>='0'&&s[i]<='9') continue;
if(s[i]=='+'||s[i]=='-'||s[i]=='*') continue;
if(s[i]=='/'||s[i]=='('||s[i]==')') continue;
return 0;
}
return 1;
}

int main()
{
char a[1010],b[1010];
int len;
Operator signs;
Number number;
InitStack_Number(&number);
InitStack_Operator(&signs);
Push_Operator(&signs,'#');
double x,y;
scanf("%s",a);
len=strlen(a);
if(check(a,len)==0)
{
printf("输入中存在多余字符\n");
exit(19);
}
a[len]='#';
int i,f=0,k=0;
Push_Operator(&signs,'#');
for(i=0; i<=len; i++)
{
if((a[i]>='0'&&a[i]<='9')||a[i]=='.')
{
b[k++]=a[i];
f=1;
continue;
}
if(f)
{
b[k]='\0';
Push_Number(&number,atof(b));
f=0;
k=0;
}
switch(compare(Gettop_Operator(&signs),a[i]))
{
case '<':
Push_Operator(&signs,a[i]);
break;
case'=':
Pop_Operator(&signs);
break;
case'>':
y=Gettop_Number(&number),Pop_Number(&number);
x=Gettop_Number(&number),Pop_Number(&number);
Push_Number(&number,Calc(x,y,Gettop_Operator(&signs)));
Pop_Operator(&signs);
i--;
break;
}
}
double ans=Gettop_Number(&number);
printf("%.2lf\n",ans);
return 0;
}