formuladecode.cpp

来自「一个基于编译原理的四则混合运算及括号运算实现的小程序」· C++ 代码 · 共 257 行

//  decode.cpp  解析基本的四则运算
#include   "string.h"   
#include   "math.h"
    
#define   ADD   1   //运算符   
#define   SUB   2   
#define   MUL   3   
#define   DIV   4   
#define   POW   5   
#define   FACT   6   
#define   LEFT   7   
#define   ADDLEVEL   1   //运算优先级别   
#define   SUBLEVEL   1   
#define   MULLEVEL   2   
#define   DIVLEVEL   2   
#define   POWLEVEL   3   
#define   FACTLEVEL   4   
#define   LEFTLEVEL   5   
    
char  string[1001];   
int   STRLEN;   
typedef   struct   stack   
{   
	float   num;//数字   
	char   opsign;//运算符   
	int   bracket;//所处括号层   
	struct   stack   *   pnext;//链表   
} stack;   
    
float   getnumber();//得到数字   
float   fact(int   n);//阶乘   
int     getlevel(int   opsign);//得到运算符的优先级别   
char    getnextopsign();//得到下一个运算符,包括'('   
void    push(char   opsign);//压入堆栈   
void    pop();//从堆栈拉出   
bool    check();//检查表达式是否合法   
stack   *getstack(int   n);//得到某堆栈指针   
    
stack   firststack;//动态堆栈首   
int     point;//表达式指针   
int     stacknum;//堆栈数目   
char    repeat='y';   
float   result;   
int     bracket;//当前层次深度   
    
    
_declspec(dllexport) double decode(char* szCode)   
{   
	bool   error=0;   
	memset(string, NULL, 1001);
	strcpy(string, szCode);

	point=0;bracket=0;stacknum=0;error=0;   
  
	STRLEN=strlen(string);   

	result=getnumber();   
	while(point<=STRLEN-1){   
	switch(string[point++]){//哪个运算符?   
	case   '+':   
	if(getnextopsign()>ADDLEVEL){   
	push(ADD);   
	result=getnumber();   
	}   
  else   result+=getnumber();   
  break;   
  case   '-':   
  if(getnextopsign()>SUBLEVEL){   
  push(SUB);   
  result=getnumber();   
  }   
  else   result-=getnumber();   
  break;   
  case   '*':   
  if(getnextopsign()>MULLEVEL){   
  push(MUL);   
  result=getnumber();   
  }   
  else   
  {   
  result*=getnumber();   
  if(stacknum>0   &&   getnextopsign()<MULLEVEL   &&   getstack(stacknum)->bracket>=bracket)   
  pop();   
  }   
  break;   
  case   '/':   
  if(getnextopsign()>DIVLEVEL){   
  push(DIV);   
  result=getnumber();   
  }   
  else   
  {   
  result/=getnumber();   
  if(stacknum>0   &&   getnextopsign()<DIVLEVEL   &&   getstack(stacknum)->bracket>=bracket)   
  pop();   
  }   
  break;   
  case   ')'://右括号   
  --bracket;   
  if(getstack(stacknum)->opsign==0){//括号前面为空   
  pop();   
  break;   
  }   
  while(stacknum>0   &&   getnextopsign()<getlevel(getstack(stacknum)->opsign)   
  &&   getstack(stacknum)->bracket>=bracket   &&   getstack(stacknum)->opsign!=0)   
  //将本层括号内可以pop的都pop   
  pop();   
  break;   
  case   '^':   
  if(getnextopsign()>POWLEVEL){   
  push(POW);   
  result=getnumber();   
  }   
  else   
  {   
  result=(float)pow((double)result,(double)getnumber());   
  while(stacknum>0   &&   getnextopsign()<getlevel(getstack(stacknum)->opsign)   
  &&   getstack(stacknum)->bracket>=bracket)   pop();   
  }   
  break;   
  case   '!':   
  if(getnextopsign()>FACTLEVEL){   
  push(FACT);   
  result=getnumber();   
  }   
  else   
  {   
  result=fact((long)result);   
  while(stacknum>0   &&   getnextopsign()<getlevel(getstack(stacknum)->opsign)   
  &&   getstack(stacknum)->bracket>=bracket)   pop();   
  }   
  break;   
  }   
  }   
  
  return result;
  
  }   

  float  getnumber()   
  {   
  if(point>STRLEN-1)   return   0;   
  char   strnum[20];   
  int   n=0;   
  if(string[point]=='-'){//一开始就是负号   
  return   0;   
  }   
  while(string[point]=='('){   
  if(string[point+1]=='-'){//负号   
  point++;   
  return   0;   
  }   
  else   if(string[point+1]=='(')   push(0);   
  else   break;   
  }   
  while((string[point]<'0'   ||   string[point]>'9')   &&   string[point]!='.')   point++;   
  while((string[point]>='0'   &&   string[point]<='9')   ||   string[point]=='.'){   
  strnum[n++]=string[point++];   
  if(point>STRLEN-1)   break;   
  }   
  strnum[n]='\0';   
  return   (float)atof(strnum);   
  }   
  char   getnextopsign()   
  {   
  int   p=point;   
  while(p<=STRLEN-1){   
  switch(string[p++]){   
  case   '+':   
  return   ADDLEVEL;   
  case   '-':   
  return   SUBLEVEL;   
  case   '*':   
  return   MULLEVEL;   
  case   '/':   
  return   DIVLEVEL;   
  case   '(':   
  return   LEFTLEVEL;   
  case   '^':   
  return   POWLEVEL;   
  case   '!':   
  return   FACT;   
  case   ')':   
  return   0;   
  }   
  }   
  return   0;   
  }   
  void   push(char   opsign)   
  {   
  stack   *p=getstack(stacknum);   
  if(stacknum>0)   p=(p->pnext=new   stack);   
  p->bracket=bracket;   
  if(string[point]=='('){   
  ++bracket;   
  point++;   
  }   
  p->num=result;   
  p->opsign=opsign;   
  stacknum++;   
  }   
  void   pop()   
  {   
  stack   *p=getstack(stacknum);   
  switch(p->opsign){   
  case   ADD:   
  result+=p->num;   
  break;   
  case   SUB:   
  result=p->num-result;   
  break;   
  case   MUL:   
  result*=p->num;   
  break;   
  case   DIV:   
  result=p->num/result;   
  break;   
  case   POW:   
  result=(float)pow(p->num,result);   
  break;   
  case   FACT:   
  result=fact((long)result);   
  break;   
  case   0:   
  break;   
  }   
  if(stacknum>1)   delete   p;   
  stacknum--;   
  }   
    
    
  float   fact(int   n)   
  {   
  float   r=1;   
  if(n<=1)   return   1;   
  while(n>1){   
  r*=n;   
  --n;   
  }   
  return   r;   
  }   
  int   getlevel(int   opsign)   
  {   
  if(opsign<=2)   return   1;   
  if(opsign<=4)   return   2;   
  return   opsign-2;   
  }   
  stack   *   getstack(int   n)   
  {   
  stack   *p=NULL;   
  if(n==0)   return   &firststack;   
  for(int   i=0;i<n;i++){   
  if(i==0)   p=&firststack;   
  else   p=p->pnext;   
  }   
  return   p;   
  }