表达式求值

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#define TRUE 1
#define FALSE 0
#define STACK_INIT_SIZE 10002

#include "iostream"
#include "cstdlib"
#include "cstdio"
#include "cstring"

using namespace std;

typedef int Status; //Status相当于 int
typedef struct Stack1 //运算符栈
{
char * base;
char * top;
}SqStack1;
typedef struct Stack2 //数字栈
{
double * base;
double * top;
}SqStack2;

//运算符栈操作
void InitStack1(SqStack1&S) //创建一个空栈
{

S.base = (char *)malloc(sizeof(char) *STACK_INIT_SIZE);
S.top = S.base;
}
Status Stack1Empty(SqStack1 S)//判断是否为空
{
if(S.top == S.base) returnTRUE;
else return FALSE;
}
void Push1(SqStack1 &S,char e )//插入元素e为新的栈顶元素
{
* S.top++ = e;
}
void Pop1(SqStack1 &S,char &e)//出栈
{
e = * --S.top ;
}
char GetTop1(SqStack1 S)
{
return *(S.top-1);
}
void TraverseStack1(SqStack1 S)//输出当前顺序表
{
char * p = S.base;
cout<<"运算栈中的元素为：";
while( p != S.top )
{
cout<<*p<<"";
p++;
}
cout<<endl;
}

//数字栈操作
void InitStack2(SqStack2&S) //创建一个空栈
{

S.base = (double *)malloc(sizeof(double) *STACK_INIT_SIZE);
S.top = S.base;
}
void Push2(SqStack2 &S,double e )//插入元素e为新的栈顶元素
{
* S.top++ = e;
}
void Pop2(SqStack2 &S,double &e)//出栈
{
e = * --S.top ;
}
double GetTop2(SqStack2 S)
{
return *(S.top-1);
}
void TraverseStack2(SqStack2 S)//输出当前顺序表
{
double * p = S.base;
cout<<"数字栈栈中的元素为：";
while( p != S.top )
{
cout<<*p<<"";
p++;
}
cout<<endl;
}

//运算操作
Status In(char ch)//判断ch是否为运算符
{
if(ch == '+' || ch == '('|| ch == '-' || ch =='*' || ch == '/' || ch == ')' || ch == '=')return TRUE;
else return FALSE;
}
char Precede(char a, char b) // 计算运算符优先级
{
char r;
switch(b)
{
  case '+':     //此处由于加减几乎优先级一样，故放在一起
  case '-' :
   if (a=='(' ||a=='=')   r = '<';
   else  r = '>';
   break;
  case '*':     //此处由于乘除优先级一样，故放在一起
  case '/' :
   if (a=='*' ||a=='/' || a==')')
   r ='>';
   else r = '<';
   break;
  case '(' : r ='<';
   break;
  case ')' :
   if (a=='(') r = '=';
   else r = '>';
   break;
  case'=':
   if (a=='=') r = '=';
   else r ='>';
   break;
}
return r;
}
double Operate(double a,char theta, double b)
{
switch (theta)
{
  case '+': return a +b;break;
  case '-': return a -b;break;
  case '*': return a *b;break;
  case '/': return a /b;break;
  default : return FALSE;
}
}
void Evaluateexpression_r()
{
cout<<"++++++++++请输入表达式，以 = 结束（例：1.000+2/4=）+++++++++++++"<<endl;
char str[300];
cin>>str;
char *p = str;
SqStack1 OPTR;
SqStack2 OPND;
InitStack1(OPTR); //设OPTR和OPND分别为运算符栈和运算数栈
InitStack2(OPND);
Push1(OPTR,'=');
char x,theta,c;
double a,b,k,t,m;
c = *p;
while( !Stack1Empty(OPTR))
{
  if(!In(c) )
  {
   for(k = 0;!In(c) && c!='.'; c = * ++p)
     k= 10*k + c-'0';
   t = 0 ;
   if(c=='.')
   {
    c= * ++p;
    for(t= 0,m = 0.1 ; !In(c) ; c = * ++p)
    {
     t+= m * (c-'0');
     m*= 0.1;
    }
   }
   Push2(OPND,k+t);
  }
  else
  {
    switch(Precede(GetTop1(OPTR),c))
    {
     case'<':
      Push1(OPTR,c);
      c= * ++p;
      break;
     case'=':
      Pop1(OPTR,x);
      c= * ++p;
      break;
     case'>':
      Pop1(OPTR,theta);
      Pop2(OPND,b);Pop2(OPND,a);
      Push2(OPND,Operate(a,theta,b));
      break;
    }
  }
}
printf("表达式结果：%s%.3lf\n",str,GetTop2(OPND));
}
int main()
{
int door = 1;
do{
  Evaluateexpression_r();
  cout<<"是否要继续检测下一组括号(Y/N)：";
  char ch;
  cin>>ch;
  if(ch == 'N'|| ch == 'n') door= 0;
}while(door);

return 0;
}

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