main.cpp

表达式求值的小程序源码,呵呵.献丑了.高手就不用看了.

#include<iostream>
#include<stdlib.h>
#include<math.h>
//-------------------------------
#define OK 1
#define ERROR 0
#define TRUE 1
#define FALSE 0
#define STACK_INIT_SIZE 100
#define STACKINCREMENT 10
//------------------------
typedef struct{
	float *base;
	float *top;
	int size;
}OpndStack;

typedef struct{
	char *base;
	char *top;
	int size;
}OptrStack;
//--------------------------------
typedef int Status;
using namespace std;


//--------------STACK OPERATE-----------------------------------------------------------------
//--------------------InitStack---------------------
Status InitStack(OpndStack &s){
	s.base=(float*)malloc(STACK_INIT_SIZE*sizeof(float));
	if(s.base==NULL)exit(OVERFLOW);
	s.top=s.base;
	s.size=STACK_INIT_SIZE;
	return(OK);
}
Status InitStack(OptrStack &s){
	s.base=(char*)malloc(STACK_INIT_SIZE*sizeof(char));
	if(s.base==NULL)exit(OVERFLOW);
	s.top=s.base;
	s.size=STACK_INIT_SIZE;
	return(OK);
}
//------------------Push-------------------------
Status Push(OpndStack &s,float e){
	if(s.top-s.base>=s.size){
		s.base=(float*)malloc(STACKINCREMENT*sizeof(float));
		if(!s.base)exit(OVERFLOW);
		s.top=s.base+s.size;
	}
	*s.top++=e;
	return(OK);
}
Status Push(OptrStack &s,char e){
	if(s.top-s.base>=s.size){
		s.base=(char*)malloc(STACKINCREMENT*sizeof(char));
		if(!s.base)exit(OVERFLOW);
		s.top=s.base+s.size;
	}
	*s.top++=e;
	return(OK);
}
//----------------------GetTop----------------------
float GetTop(OpndStack &s){
	if(s.top==s.base)return 0;
	return (*(s.top-1));
}
char GetTop(OptrStack &s){
	if(s.top==s.base)return ERROR;
	return *(s.top-1);
}
//---------------------Pop----------------
Status Pop(OpndStack &s,float &e){
	if(s.top==s.base)return ERROR;
	e=*--s.top;
	return OK;
}

Status Pop(OptrStack &s,char &e){
	if(s.top==s.base)return ERROR;
	e=*--s.top;
	return OK;
}

//---------------tell wether the charactor is an operator---------------------------------------
Status InOptr(char b){
	if(b=='+'||b=='-'||b=='*'||b=='/'||b=='('||b==')'||b=='#')
		return(TRUE);
	else
		return FALSE;
}

//-----------------------TRANSFORM CHARACTORS TO NUMBERS-------------------------------------
float transform(char *c,int &count){
	char *q;
	int n,k,l;
	float integer=0,decimal=0;
	for(q=c,n=0;!InOptr(*q)&&*q!='#';n++,q++);
	for(k=1;k<n+1&&*(c+k-1)!='.';k++);
	if(k>n)//k=n+1
		for(l=1;l<k;l++){
			integer=integer+(c[l-1]-48)*pow(10.0F,k-l-1.0F);
		}
	if(k==n){
		for(l=1;l<k;l++){
			integer=integer+(c[l-1]-48)*pow(10.0F,k-l-1.0F);
		}
	}		
	if(k<n&&k>1){
		for(l=1;l<k;l++)
			integer=integer+(c[l-1]-48)*pow(10.0F,k-l-1.0F);
		for(l=1;l<n-k+1;l++)
			decimal=decimal+(c[k+l-1]-48)*pow(10.0F,(float)(-l));
	}
	if(k==1){
		for(l=1;l<n;l++)
			decimal=decimal+(c[l]-48)*pow(10.0F,(float)(-l));
	}
	count=n;
	return(integer+decimal);

}

//--------------------get the PRI ----------------------------- ------------------------
int f(char e);
char Precede(char a,char b){
	char c[7][7]={{62,62,60,60,60,62,62},{62,62,60,60,60,62,62},
					{62,62,62,62,60,62,62},{62,62,62,62,60,62,62},
					{60,60,60,60,60,61,0},{62,62,62,62,0,62,62},
					{60,60,60,60,60,0,61}};
	return(c[f(a)][f(b)]);
}

int f(char e){
	if(e=='+')return(0);
	if(e=='-')return(1);
	if(e=='*')return 2;
	if(e=='/')return 3;
	if(e=='(')return 4;
	if(e==')')return 5;
	if(e=='#')return 6;
	else exit(0);
}

//-----------------get the answer by using the numbers and operator----------
float Operate(float a,char theta,float b)
{
	switch(theta)
	{
	case'+':
		return(a+b);
	case'-':
		return(a-b);
	case'*':
		return(a*b);
	case'/':
		return(a/b);
	default:
		cout<<"the expression have something wrong\n"<<endl;
		exit(0);
	
	}
}

//--------use the string to get the answer-------------
float EvaluateExpression(char *c,int n){
	int i=0,count;
	char theta;
	float e,a,b;
	OptrStack Optr;
	OpndStack Opnd;
	InitStack(Optr);
	InitStack(Opnd);
	Push(Optr,'#');
	while(c[i]!='#'||GetTop(Optr)!='#'){
		if(i>n){
			cout<<"You forgot add the sign'#' after the expression.Please check it and add the sign'#'at the end of the expression..\n";
			exit(0);
		}
		if(!InOptr(c[i])){
			e=transform(&c[i],count);
			i=i+count;
			Push(Opnd,e);
		}
		else
			switch(Precede(GetTop(Optr),c[i])){
			case'<':
				Push(Optr,c[i]);
				i++;
				break;
			case'=':
				Pop(Optr,theta);
				i++;
				break;
			case'>':
				Pop(Optr,theta);
				Pop(Opnd,a);
				Pop(Opnd,b);
				Push(Opnd,Operate(b,theta,a));
				break;
			}//switch
	}//while
	if(Opnd.top-Opnd.base!=1||Optr.top!=Optr.base+1){
		cout<<"sorry,the expression you input have something wrong.Please check it and reactive the program..\n";
		exit(0);
	}
	return(GetTop(Opnd));
}//EvaluateExpression

//------------main----------------
int main(){
	int n=0,i=0;
	char c[100];
	cout<<"please input the expression :\n (ending by the charator '#')"<<endl;
	for(cin>>c[0];c[n]!='#';n++,cin>>c[n]);
	for(;i<n;i++){
		if(!(InOptr(c[i])||(c[i]>47&&c[i]<58)||c[i]=='.')){
			cout<<"there are some irregular numbers in your expression.please check it and reinput."<<endl;
			exit(0);
		}
	}
	cout<<"the answer is :\n"<<EvaluateExpression(c,n)<<endl;
	return(0);
}