计算器界面需要QWidget组件作为顶层窗口，QLineEdit组件作为输入框，QPsuhButton作为按钮。
界面规划设计如下：
#include <QApplication>#include <QWidget>#include <QLineEdit>#include <QPushButton>int main(int argc, char argv[]){QApplication a(argc, argv);QWidget widget = new QWidget(NULL, Qt::WindowCloseButtonHint);//构建输入框，设置属性QLineEdit edit = new QLineEdit(widget);edit->move(10, 10);edit->resize(240, 30);edit->setReadOnly(true);//构造按钮，设置属性QPushButton button[20] = {0};const char buttontext[20] ={"7", "8", "9", "+", "(","4", "5", "6", "-", ")","1", "2", "3", "", "<-","0", ".", "=", "/", "C"};for(int i = 0; i < 4; i++){for(int j = 0; j < 5; j++){button[5i + j] = new QPushButton(widget);button[5i + j]->move(10 + (10 + 40)j, 50 + (10 + 40)i);button[5i + j]->resize(40, 40);button[5i + j]->setText(buttontext[5i + j]);}}//设置窗口int ret = 0;widget->show();widget->setFixedSize(widget->width(), widget->height());ret = a.exec();delete widget;return ret;}
二、项目代码重构
重构是以改善代码质量为目的的代码重写，使得软件的设计和架构更加合理，提高了软件的扩展性和维护性。
代码重构与代码实现的区别：
A、代码实现是按照设计编程实现，核心在于功能实现，不考虑架构的优劣
B、代码重构是以提高代码质量为目的的软件架构优化，核心在于优化架构，不考虑对已实现功能的修改。
代码重构在软件开发过程中的阶段：
代码重构的适用场合：
A、项目中重复代码越来越多
B、项目中代码功能越来越不清晰
C、项目中代码实现离设计越来越远
计算器界面代码重构：
由于需要申请堆空间资源，使用二阶构造模式。
CalculatorUI.h文件：
#ifndef CALCULATORUI_H#define CALCULATORUI_H#include <QWidget>#include <QLineEdit>#include <QPushButton>class CalculatorUI : public QWidget{Q_OBJECTpublic:static CalculatorUI newInstance();~CalculatorUI();void show();private:CalculatorUI();bool Construct();private:QLineEdit m_edit;QPushButton m_buttons[20];};#endif // CALCULATORUI_H
CalculatorUI.cpp文件：
#include "CalculatorUI.h"CalculatorUI::CalculatorUI() : QWidget(NULL, Qt::WindowCloseButtonHint){}CalculatorUI CalculatorUI::newInstance(){CalculatorUI ret = new CalculatorUI();if(NULL == ret || !ret->Construct()){delete ret;ret = NULL;}return ret;}CalculatorUI::~CalculatorUI(){}void CalculatorUI::show(){QWidget::show();setFixedSize(width(), height());}bool CalculatorUI::Construct(){bool ret = true;m_edit = new QLineEdit(this);if(m_edit != NULL){m_edit->move(10, 10);m_edit->resize(240, 30);m_edit->setReadOnly(true);}else{ret = false;}const char buttontext[20] ={"7", "8", "9", "+", "(","4", "5", "6", "-", ")","1", "2", "3", "", "<-","0", ".", "=", "/", "C"};for(int i = 0; (i < 4) && ret; i++){for(int j = 0; (j < 5) && ret; j++){m_buttons[5i + j] = new QPushButton(this);if(m_buttons[5i + j] != NULL){m_buttons[5i + j]->move(10 + (10 + 40)j, 50 + (10 + 40)i);m_buttons[5i + j]->resize(40, 40);m_buttons[5i + j]->setText(buttontext[5i + j]);}else{ret = false;}}}return ret;}
Main.cpp文件：
#include <QApplication>#include <QWidget>#include <QLineEdit>#include <QPushButton>#include "CalculatorUI.h"int main(int argc, char argv[]){QApplication a(argc, argv);CalculatorUI widget = CalculatorUI::newInstance();int ret = 0;if(widget != NULL){widget->show();ret = a.exec();delete widget;}return ret;}
三、计算器算法引擎
人类思维和阅读习惯的运算表达式为中缀表达式，但计算机的运算表达式为后缀表达式，因此需要将中缀表达式转换为后缀表达式。
算法引擎的解决方案如下：
A、将中缀表达式的数字和运算符分离
B、将中缀表达式转换为后缀表达式
C、使用后缀表达式计算运算表达式的结果
1、计算表达式的分离
中缀表达式通常包含如下元素：
A、数字与小数点[0-9 .]
B、符号位[+ -]
C、运算符[+ - /]
D、括号[( )]
分离算法设计分析：
以符号作为标识对表达式中的字符进行逐个访问
A、定义累计变量
B、当前字符为数字或小数点
累计，num += exp[i]
C、当前字符exp[i]为为符号
num为运算数，分离并保存
如果exp[i]为正负号
累计符号位+、-：num += exp[i]
如果exp[i]为运算符
分离并保存
分离算法源码：
QQueue<QString> CalculatorDec::split(const QString& exp){QQueue<QString> ret;QString pre = "";QString num = "";for(int i=0; i<exp.length(); i++){if(isDigitOrDot(exp[i])){num += exp[i];pre = exp[i];}else if(isSymbol(exp[i])){if(!num.isEmpty()){ret.enqueue(num);num.clear();}if(isSign(exp[i]) && ((pre == "") || (pre == "(") || isOperator(pre))){num += exp[i];}else{ret.enqueue(exp[i]);}pre = exp[i];}}if(!num.isEmpty()){ret.enqueue(num);}return ret;}
2、表达式的转换
中缀表达式转换为后缀表达式的注意事项：
A、运算表达式中的括号必须匹配
B、必须根据运算优先级进行转换
C、转换后的后缀表达式中不能有括号
D、转换后的后缀表达式可以计算出正确结果
在运算表达式中，括号匹配成对出现，左括号必须限于右括号出现。
匹配算法如下：
bool CalculatorDec::match(QQueue<QString>& exp){bool ret = true;int len = exp.length();QStack<QString> stack;for(int i=0; i<len; i++){if( isLeft(exp[i]) ){stack.push(exp[i]);}else if( isRight(exp[i]) ){if( !stack.isEmpty() && isLeft(stack.top()) ){stack.pop();}else{ret = false;break;}}}return ret && stack.isEmpty();}
转换过程：
A、当前元素e为数字，直接输出
B、当前元素e为运算符：
与栈顶运算符进行优先级比较，如果小于等于，将栈顶元素输出，转1；如果大于，将当前元素入栈。
C、当前元素e为左括号：入栈
D、当前元素e为右括号：
弹出栈顶元素并输出，直至栈顶元素为左括号，将栈顶的左括号从栈中弹出
转换算法如下：
bool CalculatorDec::transform(QQueue<QString>& exp, QQueue<QString>& output){bool ret = match(exp);QStack<QString> stack;output.clear();while( ret && !exp.isEmpty() ){QString e = exp.dequeue();if( isNumber(e) ){output.enqueue(e);}else if( isOperator(e) ){while( !stack.isEmpty() && (priority(e) <= priority(stack.top())) ){output.enqueue(stack.pop());}stack.push(e);}else if( isLeft(e) ){stack.push(e);}else if( isRight(e) ){while( !stack.isEmpty() && !isLeft(stack.top()) ){output.enqueue(stack.pop());}if( !stack.isEmpty() ){stack.pop();}}else{ret = false;}}while( !stack.isEmpty() ){output.enqueue(stack.pop());}if( !ret ){output.clear();}return ret;}3、结果计算
使用后缀表达式计算结果需要遍历后缀表达式中的数字和运算符。
A、当前元素为数字：进栈
B、当前元素为运算符：
从栈中弹出右操作数
从栈中弹出左操作数
根据符号进行运算
将运算结果压入栈中
遍历结束后，栈中的数字即为结果
QString CalculatorDec::calculate(QString l, QString op, QString r){QString ret = "Error";if( isNumber(l) && isNumber(r) ){double lp = l.toDouble();double rp = r.toDouble();if( op == "+" ){ret.sprintf("%f", lp + rp);}else if( op == "-" ){ret.sprintf("%f", lp - rp);}else if( op == "" ){ret.sprintf("%f", lp rp);}else if( op == "/" ){const double P = 0.000000000000001;if( (-P < rp) && (rp < P) ){ret = "Error";}else{ret.sprintf("%f", lp / rp);}}else{ret = "Error";}}return ret;}QString CalculatorDec::calculate(QQueue<QString>& exp){QString ret = "Error";QStack<QString> stack;while( !exp.isEmpty() ){QString e = exp.dequeue();if( isNumber(e) ){stack.push(e);}else if( isOperator(e) ){QString rp = !stack.isEmpty() ? stack.pop() : "";QString lp = !stack.isEmpty() ? stack.pop() : "";QString result = calculate(lp, e, rp);if( result != "Error" ){stack.push(result);}else{break;}}else{break;}}if( exp.isEmpty() && (stack.size() == 1) && isNumber(stack.top()) ){ret = stack.pop();}return ret;}
四、用户界面与业务逻辑的分离
1、计算器架构设计
软件架构一般包括：
A、用户界面模块，接收用户输入，呈现数据
B、业务逻辑模块，根据用户需求处理数据
软件的各个模块之间必须遵循高内聚、低耦合的原则，每个模块应该只实现单一的功能，模块内部的子模块只作为整体的单一功能而存在，模块间通过约定好的接口进行交互。
模块间仅通过接口进行关联，因此必然存在使用接口的模块和实现接口的模块，模块间的关系必须是单向依赖的。
计算器应用程序的架构如下：
QCalculatorUI类实现了程序界面，QCalculatorDec类实现了计算器的核心算法。QCalculatorUI类通过引入ICalculator指针类型成员变量，增加了ICalculator属性；QCalculatorDec类继承自ICalculator，实现了ICalculator接口的计算功能。QCalculatorUI类与QCalculatorDec类间没有关系。
2、ICalculator类
#ifndef ICALCULATOR_H#define ICALCULATOR_H#include <QString>class ICalculator{public:virtual bool expression(const QString & exp) = 0;virtual QString result() = 0;};#endif // ICALCULATOR_H3、QCalculatorDec类
QCalculatorDec类继承自ICalculator，实现ICalculator类的计算功能
QCalculatorDec.h文件：
#ifndef CALCULATORDEC_H#define CALCULATORDEC_H#include <QString>#include <QQueue>#include <QStack>#include "ICalculator.h"class CalculatorDec : public ICalculator{public:CalculatorDec();~CalculatorDec();bool expression(const QString & exp);QString expression();QString result();private:bool isDigitOrDot(QChar c);bool isSymbol(QChar c);bool isSign(QChar c);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);bool match(QQueue<QString>& exp);bool transform(QQueue<QString>& exp, QQueue<QString>& output);QString calculate(QQueue<QString>& exp);QString calculate(QString l, QString op, QString r);private:QString m_exp;QString m_result;};#endif // CALCULATORDEC_H
QCalculatorDec.cpp文件：
#include "CalculatorDec.h"CalculatorDec::CalculatorDec(){m_exp = "";m_result = "";}CalculatorDec::~CalculatorDec(){}bool CalculatorDec::expression(const QString & exp){bool ret = false;QQueue<QString> spExp = split(exp);QQueue<QString> postExp;m_exp = exp;if( transform(spExp, postExp) ){m_result = calculate(postExp);ret = (m_result != "Error");}else{m_result = "Error";}return ret;}QString CalculatorDec::expression(){QString ret;return ret;}QString CalculatorDec::result(){return m_result;}bool CalculatorDec::isDigitOrDot(QChar c){return ('0' <= c) && (c <= '9') || (c == '.');}bool CalculatorDec::isSymbol(QChar c){return isOperator(c) || ('(' == c) || (')' == c);}bool CalculatorDec::isSign(QChar c){return ('+' == c) || ('-' == c);}bool CalculatorDec::isNumber(QString s){bool ret = false;s.toDouble(&ret);return ret;}bool CalculatorDec::isOperator(QString s){return ("+" == s) || ("-" == s) || ("" == s) || ("/" == s);}bool CalculatorDec::isLeft(QString s){return ("(" == s);}bool CalculatorDec::isRight(QString s){return (")" == s);}int CalculatorDec::priority(QString s){int ret = -1;if(s == "+" || s == "-"){ret = 1;}if(s == "" || s == "/"){ret = 2;}return ret;}QQueue<QString> CalculatorDec::split(const QString& exp){QQueue<QString> ret;QString pre = "";QString num = "";for(int i=0; i<exp.length(); i++){if(isDigitOrDot(exp[i])){num += exp[i];pre = exp[i];}else if(isSymbol(exp[i])){if(!num.isEmpty()){ret.enqueue(num);num.clear();}if(isSign(exp[i]) && ((pre == "") || (pre == "(") || isOperator(pre))){num += exp[i];}else{ret.enqueue(exp[i]);}pre = exp[i];}}if(!num.isEmpty()){ret.enqueue(num);}return ret;}bool CalculatorDec::match(QQueue<QString>& exp){bool ret = true;int len = exp.length();QStack<QString> stack;for(int i=0; i<len; i++){if( isLeft(exp[i]) ){stack.push(exp[i]);}else if( isRight(exp[i]) ){if( !stack.isEmpty() && isLeft(stack.top()) ){stack.pop();}else{ret = false;break;}}}return ret && stack.isEmpty();}bool CalculatorDec::transform(QQueue<QString>& exp, QQueue<QString>& output){bool ret = match(exp);QStack<QString> stack;output.clear();while( ret && !exp.isEmpty() ){QString e = exp.dequeue();if( isNumber(e) ){output.enqueue(e);}else if( isOperator(e) ){while( !stack.isEmpty() && (priority(e) <= priority(stack.top())) ){output.enqueue(stack.pop());}stack.push(e);}else if( isLeft(e) ){stack.push(e);}else if( isRight(e) ){while( !stack.isEmpty() && !isLeft(stack.top()) ){output.enqueue(stack.pop());}if( !stack.isEmpty() ){stack.pop();}}else{ret = false;}}while( !stack.isEmpty() ){output.enqueue(stack.pop());}if( !ret ){output.clear();}return ret;}QString CalculatorDec::calculate(QString l, QString op, QString r){QString ret = "Error";if( isNumber(l) && isNumber(r) ){double lp = l.toDouble();double rp = r.toDouble();if( op == "+" ){ret.sprintf("%f", lp + rp);}else if( op == "-" ){ret.sprintf("%f", lp - rp);}else if( op == "" ){ret.sprintf("%f", lp rp);}else if( op == "/" ){const double P = 0.000000000000001;if( (-P < rp) && (rp < P) ){ret = "Error";}else{ret.sprintf("%f", lp / rp);}}else{ret = "Error";}}return ret;}QString CalculatorDec::calculate(QQueue<QString>& exp){QString ret = "Error";QStack<QString> stack;while( !exp.isEmpty() ){QString e = exp.dequeue();if( isNumber(e) ){stack.push(e);}else if( isOperator(e) ){QString rp = !stack.isEmpty() ? stack.pop() : "";QString lp = !stack.isEmpty() ? stack.pop() : "";QString result = calculate(lp, e, rp);if( result != "Error" ){stack.push(result);}else{break;}}else{break;}}if( exp.isEmpty() && (stack.size() == 1) && isNumber(stack.top()) ){ret = stack.pop();}return ret;}
4、CalculatorUI类
CalculatorUI类使用ICalculator接口的计算功能。通过在CalculatorUI类中引入ICalculator指针成员变量，增加了ICalculator属性。将所有按钮发送的信号与onCalculate()槽函数连接。
CalculatorUI.h文件：
#ifndef CALCULATORUI_H#define CALCULATORUI_H#include <QWidget>#include <QLineEdit>#include <QPushButton>#include "icalculator.h"class CalculatorUI : public QWidget{Q_OBJECTpublic:static CalculatorUI newInstance();~CalculatorUI();void show();void setCalculator(ICalculator cal);ICalculator getCalculator();private:CalculatorUI();bool Construct();private slots:void onCalculate();private:QLineEdit m_edit;QPushButton m_buttons[20];ICalculator m_cal;};#endif // CALCULATORUI_H
CalculatorUI.cpp文件：
#include "CalculatorUI.h"CalculatorUI::CalculatorUI() : QWidget(NULL, Qt::WindowCloseButtonHint){m_cal = NULL;}CalculatorUI CalculatorUI::newInstance(){CalculatorUI ret = new CalculatorUI();if(NULL == ret || !ret->Construct()){delete ret;ret = NULL;}return ret;}CalculatorUI::~CalculatorUI(){}void CalculatorUI::show(){QWidget::show();setFixedSize(width(), height());}bool CalculatorUI::Construct(){bool ret = true;m_edit = new QLineEdit(this);if(m_edit != NULL){m_edit->move(10, 10);m_edit->resize(240, 30);m_edit->setReadOnly(true);}else{ret = false;}const char buttontext[20] ={"7", "8", "9", "+", "(","4", "5", "6", "-", ")","1", "2", "3", "", "<-","0", ".", "=", "/", "C"};for(int i = 0; (i < 4) && ret; i++){for(int j = 0; (j < 5) && ret; j++){m_buttons[5i + j] = new QPushButton(this);if(m_buttons[5i + j] != NULL){m_buttons[5i + j]->move(10 + (10 + 40)j, 50 + (10 + 40)i);m_buttons[5i + j]->resize(40, 40);m_buttons[5i + j]->setText(buttontext[5i + j]);connect(m_buttons[5i + j], SIGNAL(clicked()), this, SLOT(onCalculate()));}else{ret = false;}}}return ret;}void CalculatorUI::setCalculator(ICalculator cal){m_cal = cal;}ICalculator CalculatorUI::getCalculator(){return m_cal;}void CalculatorUI::onCalculate(){QPushButton button = dynamic_cast<QPushButton>(sender());if( button != NULL ){QString buttontext = button->text();if( buttontext == "<-" ){QString text = m_edit->text();if( text.length() > 0 ){text.remove(text.length()-1, 1);m_edit->setText(text);}}else if( buttontext == "C" ){m_edit->setText("");}else if( buttontext == "=" ){if( m_cal != NULL ){m_cal->expression(m_edit->text());m_edit->setText(m_cal->result());}}else{m_edit->setText(m_edit->text() + buttontext);}}}
5、Calculator类
计算器Calculator类包含计算器程序界面CalculatorUI和核心算法CalculatorDec两部分。在Calculator构造过程中需要指定CalculatorUI对应的核心算法CalculatorDec。
Calculator.h文件：
#ifndef CALCULATOR_H#define CALCULATOR_H#include "CalculatorUI.h"#include "CalculatorDec.h"class Calculator{private:CalculatorUI m_ui;CalculatorDec m_cal;Calculator();bool construct();public:static Calculator newInstance();void show();~Calculator();};
#endif // CALCULATOR_H
Calculator.cpp文件：
#include "Calculator.h"Calculator::Calculator(){}bool Calculator::construct(){m_ui = CalculatorUI::newInstance();if(m_ui != NULL){m_ui->setCalculator(&m_cal);}return (m_ui != NULL);}Calculator Calculator::newInstance(){Calculator ret = new Calculator();if((ret == NULL) || (!ret->construct())){delete ret;ret = NULL;}return ret;}void Calculator::show(){m_ui->show();}Calculator::~Calculator(){delete m_ui;}
6、使用实例
Main.cpp文件：
#include <QApplication>#include "Calculator.h"int main(int argc, char argv[]){QApplication a(argc, argv);Calculator cal = Calculator::newInstance();int ret = 0;if(cal != NULL){cal->show();ret = a.exec();delete cal;}return ret;}
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