第12课 计算器核心解析算法（上）

5 + 3 → 5 3 +

1 + 2 * 3 → 1 2 3 * +

9 + （3 – 1）* 5 → 9 3 1 – 5 * +

#ifndef QCALCULATORDEC_H
#define QCALCULATORDEC_H

#include <QString>
#include <QStack>
#include <QQueue>

class QCalculatorDec
{
protected:
    QString m_exp;
    QString m_result;

    bool isDigitOrDot(QChar c);
    bool isSymbol(QChar c); //操作符或左右括号
    bool isSign(QChar c);   //符号位+或-
    bool isNumber(QString s);
    bool isOperator(QString s);
    bool isLeft(QString s);
    bool isRight(QString s);
    int priority(QString s);

    QQueue<QString> split(const QString& exp);

 public:
    QCalculatorDec();
    ~QCalculatorDec();

    bool expression(const QString& exp);
    QString expression();
    QString result();
};

#endif // QCALCULATORDEC_H

#include "QCalculatordec.h"

#include <QDebug>

QCalculatorDec::QCalculatorDec()
{
    m_exp = "";
    m_result = "";

    QQueue<QString> r = split("+9.11 + (-3 - -1) * -5");

    for(int i = 0;i < r.length(); i++)
    {
        qDebug() << r[i];
    }
}

QCalculatorDec::~QCalculatorDec()
{

}

bool QCalculatorDec::isDigitOrDot(QChar c)
{
    return (('0' <= c) && (c <= '9')) || (c == '.');
}

bool QCalculatorDec::isSymbol(QChar c)
{
  return isOperator(c) || (c =='(') || (c == ')');
}

bool QCalculatorDec::isSign(QChar c)
{
    return (c == '+') || (c == '-');
}

bool QCalculatorDec::isNumber(QString s)
{
    bool ret = false;
    s.toDouble(&ret); //将字符串转为数字
    return ret;
}

bool QCalculatorDec::isOperator(QString s)
{
    return (s == "+") || (s == "-") ||(s == "*") ||(s == "/");
}

bool QCalculatorDec::isLeft(QString s)
{
    return (s == "(");
}

bool QCalculatorDec::isRight(QString s)
{
    return (s == ")");
}

int QCalculatorDec::priority(QString s)
{
    int ret = 0;

    if((s == "+") || (s =="-"))
    {
        ret = 1;
    }else if((s == "*") || (s == "/"))
    {
        ret = 2;
    }
    return ret;
}

bool QCalculatorDec::expression(const QString &exp)
{
    bool ret =false;

    return ret;
}

QString QCalculatorDec::result()
{
    return m_result;
}

QQueue<QString> QCalculatorDec::split(const QString& exp)
{
    QQueue<QString> ret;
    QString num = "";
    QString pre = "";

    for(int i=0; i<exp.length(); i++)
    {
        //数字或小数点
        if(isDigitOrDot(exp[i])){
            num +=exp[i];
            pre = exp[i];
        //标识符（操作符、左右括号），其它字符（如空格）会被跳过
        }else if(isSymbol(exp[i])){
            //遇标识符时，表示读到的己经不是数字了，就将num分离并保存起来
            if(!num.isEmpty())
            {
                ret.enqueue(num);//num进队列，保存起来
                num.clear();
            }

            //如果当前这个非数字的标识符是+或-，则进一步判断是正负号，还是运算符
            //当+或-的前一个有效字符为空、左括号或运算符时，这时他们表示正负号。如+9、(-3、5- -3
            if(isSign(exp[i]) && ((pre =="") || (pre == "(") || isOperator(pre)))
            {
                num +=exp[i];
            }
            else
            {
                //运算符或左右括号等符号进队列
                ret.enqueue(exp[i]);
            }
            pre = exp[i]; //读完一个字符
        }
    }

    //读完所有的字符，最后一个数字型的串入队列
    if(!num.isEmpty())
    {
        ret.enqueue(num);
    }

    return ret;
}