calculator.cpp

a simple game vc＋＋写的 24 点小游戏

///////本程序完成简易的calculator，为用户输入做准备！
#include "stdlib.h"
#include "conio.h"
#define MAX_STACK_SIZE 50
#define MAX_EXPR_SIZE 50
enum  precedence{lparen,rparen,plus,minus,times,divide,eos,operand};
static int isp[7]={0,19,12,12,13,13,0};
static int icp[7]={20,19,12,12,13,13,0};
//expr 是前缀表达式以等于号结束！
char expr[MAX_EXPR_SIZE];
//string 是后缀表达式
char string[MAX_EXPR_SIZE];
//length 是string 的长度
int length=0;
precedence pstack[MAX_STACK_SIZE];
float stack[MAX_STACK_SIZE];
short poke[4];

///////////////////////////////////////
void add(int &top,float p)
{
	if(top<49)
		stack[++top]=p;
	else
		exit(-1);
	
}

float  del(int &top)
{	
	if(top==-1)
		exit(0);
	else
		return stack[top--];
}
//////////////////////////////////////////////
void add(int &top,precedence poke)
{	
	if(top<49)
		pstack[++top]=poke;
	else 
		exit(-1);
}

precedence delt(int &top)
{	
	if(top==-1)
		exit(-1);
	else
		return pstack[top--];
}

char print_token(precedence token)
{	
	switch(token)
	{
	case lparen:return '(';
	case rparen:return ')';
	case plus:	return '+';
	case minus: return '-';
	case times:	return '*';
	case divide:return '/';
	case eos:	return '=';
	default :return NULL ;
	}
	
}

precedence get_token(char&symbol,int &n)
{
	
	symbol=expr[n++];
	switch(symbol)
	{
	case '(':return lparen;
	case ')':return rparen;
	case '+':return plus;
	case '-':return minus;
	case '*':return times;
	case '/':return divide;
	case '=':return eos;
	default :return operand;
	}
}
void postfix( )
{
	char symbol;
	precedence token;
	int n=0;
	pstack[0]=eos;
	int top=0;
	for(token=get_token(symbol,n);token!=eos;token=get_token(symbol,n))
	{	
		if(token==operand)
			string[length++]=symbol;	
		
		else if(token==rparen)
		{		
			while(pstack[top]!=lparen)
			{	
				string[length++]=print_token(delt(top));
			}
			delt(top);
		}
		
		else{
			while(isp[pstack[top]]>=icp[token])
				string[length++]=print_token(delt(top));
			add(top,token);
			}
	}
	while((int)(token=delt(top))!=(int)eos)
	{	
		string[length++]=print_token(token);
	}
	string[length++]='=';
	string[length]=NULL;
}

precedence gettoken(char&symbol,int &n)
{
	
	symbol=string[n++];
	switch(symbol)
	{
	case '+':return plus;
	case '-':return minus;
	case '*':return times;
	case '/':return divide;
	case '=':return eos;
	default :return operand;
	}
}

float eval()
{
	precedence token;
	char symbol;
	float op1;
	float op2;
	int n=0;
	int top=-1;
	token=gettoken(symbol,n);//应用
	while(token!=eos)
	{	
		if(token==operand)
			add(top,poke[(int)symbol-48]);//应用
		
		else{
			op2=del(top);
			op1=del(top);
			switch(token)
				{
				case plus:add(top,op1+op2);break;
				case minus: add(top,op1-op2);break;
				case times: add(top,op1*op2);break;
				case divide: add(top,op1/op2);break;
				}
			}
		token=gettoken(symbol,n);
	}

	return del(top);
}