（2）如果X是运算符，再分以下情况： a）如果栈为空，直接入栈。 b）如果X==”（“，直接入栈。 c）如果X==”）“，则将栈里的元素逐个出栈，并入队到后缀表达式队列中，直到第一个配对的”(”出栈。（注：“(”和“)”都不入队） d）如果是其他操作符（+ - * /）,则和栈顶元素进行比较优先级。如果栈顶元素的优先级大于等于X，则出栈并把栈中弹出的元素入队，直到栈顶元素的优先级小于X或者栈为空。弹出完这些元素后，才将遇到的操作符压入到栈中。

(3)最后将栈中剩余的操作符全部入队。

II 后缀表达式求解

首先准备一个栈Res_Stack.

1、从左开始向右遍历后缀表达式的元素。

2、如果取到的元素是操作数，直接入栈Res_Stack，如果是运算符，从栈中弹出2个数进行运算，然后把运算结果入栈

3、当遍历完后缀表达式时，计算结果就保存在栈里了。

二实验设计过程

1.界面设计

 font: bold 14px;
    padding: 6px;
background-color: rgb(30, 155, 144)

21个PushButton，1个Label 和设置相应的格式

历史记录面板


//展开历史对话框
void Widget::on_Button_history_clicked()
{
    if(isOpen==false){
        history_dia.show();
        isOpen=true;
    }
    else if(isOpen==true){
        history_dia.close();
        isOpen=false;
    }
}
//将结果添加到“历史”对话框的最后并换行
    history_dia.ui->textBrowser->setText
            (history_dia.ui->textBrowser->document()->toPlainText()+expression+"="+QString::number(Ans)+"\n");

2. 信号与槽的连接

1.信号

private slots:
    void on_Button_1_clicked();

    void on_Button_2_clicked();

    void on_Button_3_clicked();

    void on_Button_4_clicked();

    void on_Button_5_clicked();

    void on_Button_6_clicked();

    void on_Button_8_clicked();

    void on_Button_7_clicked();

    void on_Button_9_clicked();

    void on_Button_add_clicked();

    void on_Button_0_clicked();

    void on_Button_point_clicked();

    void on_Button_subtract_clicked();

    void on_Button_multiply_clicked();

    void on_Button_divide_clicked();

    void on_Button_clear_clicked();

    void on_Button_back_clicked();

    void on_Button_equal_clicked();

    void on_Button_left_clicked();

    void on_Button_right_clicked();

    void on_Button_history_clicked();

2.通过对槽函数的限制实现算数表达式的正确性检验

（1）当钱输入是0到9时，如果上个符号是右括号则不输入数字

void Widget::on_Button_1_clicked()
{  int i=expression.length()-1;
    if(expression .length()==0){
        Expression += "1";
        expression += "1";
        ui->Screen->setText(expression);
    }
      else if(expression.at(i) == ")")
      {
         ui->Screen->setText(expression);
               }
    else{
    Expression += "1";
    expression += "1";
    ui->Screen->setText(expression);}
}

void Widget::on_Button_2_clicked()
{
    int i=expression.length()-1;
    if(expression .length()==0){
        Expression += "2";
        expression += "2";
        ui->Screen->setText(expression);
    }
      else if(expression.at(i) == ")")
      {
         ui->Screen->setText(expression);
               }
       else{
       Expression += "2";
       expression += "2";
       ui->Screen->setText(expression);}
}

void Widget::on_Button_3_clicked(){
    int i=expression.length()-1;
    if(expression .length()==0){
        Expression += "3";
        expression += "3";
        ui->Screen->setText(expression);
    }
      else if(expression.at(i) == ")")
      {
         ui->Screen->setText(expression);
               }
       else{
       Expression += "3";
       expression += "3";
       ui->Screen->setText(expression);}
}

void Widget::on_Button_4_clicked()
{
    int i=expression.length()-1;
    if(expression .length()==0){
        Expression += "4";
        expression += "4";
        ui->Screen->setText(expression);
    }
      else if(expression.at(i) == ")")
      {
         ui->Screen->setText(expression);
               }
       else{
       Expression += "4";
       expression += "4";
       ui->Screen->setText(expression);}
}

void Widget::on_Button_5_clicked()
{
    int i=expression.length()-1;
    if(expression .length()==0){
        Expression += "5";
        expression += "5";
        ui->Screen->setText(expression);
    }
      else if(expression.at(i) == ")")
      {
         ui->Screen->setText(expression);
               }
       else{
       Expression += "5";
       expression += "5";
       ui->Screen->setText(expression);}
}

void Widget::on_Button_6_clicked()
{
    int i=expression.length()-1;
    if(expression .length()==0){
        Expression += "6";
        expression += "6";
        ui->Screen->setText(expression);
    }
      else if(expression.at(i) == ")")
      {
         ui->Screen->setText(expression);
               }
       else{
       Expression += "6";
       expression += "6";
       ui->Screen->setText(expression);}
}

void Widget::on_Button_8_clicked(){
    int i=expression.length()-1;
    if(expression .length()==0){
        Expression += "8";
        expression += "8";
        ui->Screen->setText(expression);
    }
      else if(expression.at(i) == ")")
      {
         ui->Screen->setText(expression);
               }

       else{
       Expression += "8";
       expression += "8";
       ui->Screen->setText(expression);}
}

void Widget::on_Button_7_clicked()
{  int i=expression.length()-1;
    if(expression .length()==0){
        Expression += "7";
        expression += "7";
        ui->Screen->setText(expression);
    }
      else if(expression.at(i) == ")")
      {
         ui->Screen->setText(expression);
               }

       else{
       Expression += "7";
       expression += "7";
       ui->Screen->setText(expression);}
}

void Widget::on_Button_9_clicked()
{
    int i=expression.length()-1;
    if(expression .length()==0){
        Expression += "9";
        expression += "9";
        ui->Screen->setText(expression);
    }
      else if(expression.at(i) == ")")
      {
         ui->Screen->setText(expression);
               }
       else{
       Expression += "9";
       expression += "9";
       ui->Screen->setText(expression);}
}

void Widget::on_Button_add_clicked()
{int i =expression .length() - 1;
    if(expression .length()==0|| expression.at(i) == "(" ){
    Expression += "0~+~";
    expression += "+";
    ui->Screen->setText(expression);}
    else if (expression.at(i) == "+"|| expression.at(i) == "-" || expression.at(i) == "*" || expression.at(i) == "/")
    {
        ui->Screen->setText(expression);
    }
    else{
        Expression += "~+~";
        expression += "+";
        ui->Screen->setText(expression);
    }
}

void Widget::on_Button_0_clicked()
{
    int i=expression.length()-1;
    if(expression .length()==0){
        Expression += "0";
        expression += "0";
        ui->Screen->setText(expression);
    }
      else if(expression.at(i) == ")")
      {
         ui->Screen->setText(expression);
               }
       else{
       Expression += "0";
       expression += "0";
       ui->Screen->setText(expression);}
}

（2）对小数点的正确性检验，如果多个小数点则只输入一个，如果前面又括号和操作符，则不输入，如果小数点前无数字，则在小数点前补0

//如果当前按钮是 ‘.’如果前面有括号操作符小数点什么也不做
void Widget::on_Button_point_clicked()
{//如果小数点前无数字，则补0
  int i =expression .length() - 1;
        if(expression.length()==0||(expression.at(i) == "+"|| expression.at(i) == "-" || expression.at(i) == "*" || expression.at(i) == "/"|| expression.at(i) == "(" )){
        Expression += "0.";
        expression += ".";
        ui->Screen->setText(expression);
   }
       //如果是右括号则不输入
        else if(expression.at(i) == ")"||expression.at(i) == ".")
        {
            ui->Screen->setText(expression);
        }
         //如果数字中有了小数点，则不输入
       else {
                  int falg1=0;//设置标志
                  int j;
                  //判断字符中是否有".",j为数字首字符串位置
                  for( j=expression .length() - 1;j>0;j--){
                      if(expression.at(j) == "+"|| expression.at(j) == "-" || expression.at(j) == "*" || expression.at(j) == "/"|| expression.at(j) == "(" || expression.at(j) == ")")
                           break;
                  }
                  //判断数字字符串是否已经有"."
                  for(int t=expression .length() - 1;t>j;t--)
                      if(expression.at(t) == "."){
                          falg1=1;
                      }
                  //如果有则什么也不输出
                  if(falg1==1){
                          ui->Screen->setText(expression);
                  }
                  //否则输出点
                  else{
                      Expression += ".";
                      expression += ".";
                     ui->Screen->setText(expression);
                  }
              }
}

（3）加减乘除输入的正确性检验，如果前面无输入或者时左括号则补0 ，连续输入运算符，则不输入

void Widget::on_Button_add_clicked()
{int i =expression .length() - 1;
    if(expression .length()==0|| expression.at(i) == "(" ){//如果前面无输入或者时左括号则补0
    Expression += "0~+~";
    expression += "+";
    ui->Screen->setText(expression);}
    //连续输入运算符，则不输入
    else if (expression.at(i) == "+"|| expression.at(i) == "-" || expression.at(i) == "*" || expression.at(i) == "/")
    {
        ui->Screen->setText(expression);
    }
    else{
        Expression += "~+~";
        expression += "+";
        ui->Screen->setText(expression);
    }
}

void Widget::on_Button_subtract_clicked()
{int i =expression .length() - 1;
    if(expression.length()==0|| expression.at(i) == "(" ){
    Expression += "0~-~";
    expression += "-";
    ui->Screen->setText(expression);
    }
    else if (expression.at(i) == "+"|| expression.at(i) == "-" || expression.at(i) == "*" || expression.at(i) == "/")
    {
        ui->Screen->setText(expression);
    }
    else{
        Expression += "~-~";
        expression += "-";
        ui->Screen->setText(expression);
    }
}

void Widget::on_Button_multiply_clicked()
{
       int i =expression .length() - 1;
        if(expression.length()==0|| expression.at(i) == "(" ){
        Expression += "1~*~";
        expression += "*";
        ui->Screen->setText(expression);
        }
        else if (expression.at(i) == "+"|| expression.at(i) == "-" || expression.at(i) == "*" || expression.at(i) == "/")
        {
            ui->Screen->setText(expression);
        }
        else{
            Expression += "~*~";
            expression += "*";
            ui->Screen->setText(expression);
        }
}

void Widget::on_Button_divide_clicked()
{

    int i =expression .length() - 1;
     if(expression.length()==0||expression.at(i) == "("){//如果前面无输入或者时左括号不输入
     ui->Screen->setText(expression);
     }
     else if (expression.at(i) == "+"|| expression.at(i) == "-" || expression.at(i) == "*" || expression.at(i) == "/")
     {
         ui->Screen->setText(expression);
     }
     else{
         Expression += "~/~";
         expression += "/";
         ui->Screen->setText(expression);
     }
}

（4）等号事件响应空字符和缺少操作数不输出补全右括号把结果加到历史记录里，并输出算术表达式和结果

//等号按钮点击事件
void Widget::on_Button_equal_clicked()
{   //空字符输入 缺少操作数则不输入，也不输出
    int i=expression.length()-1;
    if (expression.length() == 0||expression.at(i) == "+"|| expression.at(i) == "-" || expression.at(i) == "*" || expression.at(i) == "/")
   {
        return;
    }
    else if(expression.length() != 0){
    //补全右括号
    int count1=0;
    int count2=0;
    for(int j=expression .length() - 1;j>=0;j--){
        if(expression.at(j)=="("){
            count1++;
        }
      else if(expression.at(j)==")"){
            count2++;
        }
    }
    if(count1>count2){
        int t=count1-count2;
        while(t>0){
            expression += ")";
            Expression += "~)~";
            t--;
        }
    }
    }
    //将Expression分割，存入字符串数组ex中。ex最后一位为"#"
    QStringList ex=Expression.split("~");
    ex.insert(ex.length(),"#");
    //计算
    double Ans=this->Run(this->Transform(ex));

    //将结果添加到“历史”对话框的最后并换行
    history_dia.ui->textBrowser->setText
            (history_dia.ui->textBrowser->document()->toPlainText()+expression+"="+QString::number(Ans)+"\n");
    //将两个E/expression归零
    expression.clear();
    Expression.clear();
}

（5）括号限制输入，如果上一个是数字和右括号则当前左括号不输入，如果上一个是运算符，括号是，则当前右括号不输入。如果当前算数表达式中左括号的数量小于等于右括号的数量，则当前右括号不输入。

//左括号限制输入
void Widget::on_Button_left_clicked()
{
    int i;
    i=expression .length();
if(expression.length()==0){
    expression += "(";
    Expression += "~(~";
    ui->Screen->setText(expression);
}


else if(expression.at(i-1) == "+"|| expression.at(i-1) == "-" || expression.at(i-1) == "*" || expression.at(i-1) == "/"||expression.at(i-1) == "(")
        {
    expression += "(";
    Expression += "~(~";
    ui->Screen->setText(expression);
}

else{
    ui->Screen->setText(expression);
}
}
//右括号限制输入

void Widget::on_Button_right_clicked()
{
   // int flag1=0;
    int i=expression.length();
    int count1=0;
    int count2=0;
    for(int j=expression .length() - 1;j>=0;j--){
        if(expression.at(j)=="("){
            count1++;
        }
      else  if(expression.at(j)==")"){
            count2++;
        }
    }
    if(expression.length()==0){
        ui->Screen->setText(expression);
    }
   else if(expression.at(i-1) == "+"|| expression.at(i-1) == "-" || expression.at(i-1) == "*" || expression.at(i-1) == "/"||expression.at(i-1)==")"||expression.at(i-1)=="("){

            ui->Screen->setText(expression);
        }
    else if(count1>count2){
        expression += ")";
        Expression += "~)~";
        ui->Screen->setText(expression);
    }

}

3. 算法实现

中缀表达式转后缀表达式

//中缀转换成后缀表达式
QStringList Widget::Transform(QStringList ex){

    QStack<QString> stack;
    stack.push("#");
    QString r;

    QStringList anssss;

    for(int i=0;!stack.isEmpty();){
        //如果ex[i]是操作数，则存入r中，直到遇到操作符为止。
        if(ex[i]!="+"&&ex[i]!="-"&&ex[i]!="*"&&ex[i]!="/"&&ex[i]!="%"
                &&ex[i]!="("&&ex[i]!=")"&&ex[i]!="#"){
            anssss.insert(i,ex[i]);
            i++;

        }
        //遇到了操作符时：
        else {


            //接下来处理操作符ex[i]

            //若栈外操作符ex[i]优先级大于栈内操作符stack.top()优先级，则ex[i]进栈
            if(icp(ex[i])>isp(stack.top())){
                stack.push(ex[i]);
                i++;
            }

            //若栈外操作符优先级小于栈内操作符优先级，则将栈内操作符输出到后缀表达式，并出栈。
            else if(icp(ex[i])<isp(stack.top()))
            {
                QString x=stack.top();
                anssss.insert(i,x);
                stack.pop();
            }
            //若栈外栈内优先级相同，退栈不输出。同时，如果栈内是“（“，则读取下一字符
            else if(icp(ex[i])==isp(stack.top())){
                QString pop=stack.top();
                stack.pop();
                if(pop=="(")
                    i++;
            }
        }
    }
    return anssss;
}

后缀表达式的计算

 //取出两个操作数
    bool Widget::GetOperand(double& left,double& right){
        right=s.top();
        s.pop();
        left=s.top();
        s.pop();
    }
//开始计算
double Widget::Run(QStringList exx){
    int i=0;double l,r;
    while(i<exx.length()){
        if(exx[i]!=""&&exx[i]!="+"&&exx[i]!="-"&&exx[i]!="*"&&exx[i]!="/"){
            //操作数进栈
            s.push(exx[i].toDouble());
            i++;
        }
        else if(exx[i]!=""){
            if(exx[i]=="+"){
                this->GetOperand(l,r);
                s.push(l+r);
                i++;
            }
            else if(exx[i]=="-"){
                this->GetOperand(l,r);
                s.push(l-r);
                i++;
            }
            else if(exx[i]=="*"){
                this->GetOperand(l,r);
                s.push(l*r);
                i++;
            }
            else if(exx[i]=="/"){
                this->GetOperand(l,r);
                s.push(l/r);
                i++;
            }


        }
        else{
            i++;
        }
    }

    double ans=s.top();
    s.pop();
    //将“历史”对话框中的label文本改变。
    history_dia.ui->label->setText("历史记录:");
    ui->Screen->setText(expression+"="+QString::number(ans));
    return ans;
}

项目文件结构

类的定义

#ifndef WIDGET_H
#define WIDGET_H

#include <QWidget>
#include <QString>
#include <QStack>
#include <QDialog>
#include "history.h"
#include <QIcon>


namespace Ui {
class Widget;
}

class Widget : public QWidget
{
    Q_OBJECT

public:
    explicit Widget(QWidget *parent = nullptr);
    ~Widget();
    void paintEvent(QPaintEvent *event);

private slots:
    void on_Button_1_clicked();

    void on_Button_2_clicked();

    void on_Button_3_clicked();

    void on_Button_4_clicked();

    void on_Button_5_clicked();

    void on_Button_6_clicked();

    void on_Button_8_clicked();

    void on_Button_7_clicked();

    void on_Button_9_clicked();

    void on_Button_add_clicked();

    void on_Button_0_clicked();

    void on_Button_point_clicked();

    void on_Button_subtract_clicked();

    void on_Button_multiply_clicked();

    void on_Button_divide_clicked();

    void on_Button_clear_clicked();

    void on_Button_back_clicked();

    void on_Button_equal_clicked();

    void on_Button_left_clicked();

    void on_Button_right_clicked();

    void on_Button_history_clicked();
private:
    Ui::Widget *ui;

    //储存两个表达式
    QString expression;
    QString Expression;

    //建立“历史记录”对话框的对象
    history history_dia;
    //判断“历史记录”对话框是否打开
    bool isOpen;
private:
    //下面的函数可以将中缀表达式转换为后缀表达式

    //运算符s位于栈外的优先级
    int icp(QString s);

    //运算符s位于栈内的优先级
    int isp(QString s);

    //将分割后的字符串作为参数，返回后缀表达式。
    QStringList Transform(QStringList ex);


    //实现后缀表达式的计算
private:
    QStack<double> s;

    //开始计算
    double Run(QStringList exx);

    //计算当前运算符ch
    void calculate(char ch);

    //从栈中取出两个操作数left和rigth
    bool GetOperand(double& left,double& right);



};

#endif // WIDGET_H

四测试

简单计算器测试

五打包发布

参考视频最新QT从入门到实战完整版|传智教育_哔哩哔哩_bilibili

打包完成。

原文链接：https://blog.csdn.net/qq_57577960/article/details/121534965

一 实验准备

1.编程语言及开发环境的选择

2.实现方法

中缀转后缀，后缀表达式求解

二 实验设计过程