环境：VS集成Qt5.8
计算器功能：对整数实现+、-、*、/、清空编辑框五个小功能。
先看效果图：
先说一下思路：
第一步：创建Qt工程
第二步：创建需要的控件，并放在布局中
第三步：实现信号和槽的连接
第四步：实现槽函数
ok，其实Qt不过是一个框架，而且让你实现起来比java语言更容易。
一：创建Qt工程，工程名calculator，继承QDialog,如下图：
为了练练手，就没有使用Ui设计师了，所以看看这个目录，只有三个主要的文件：
1：calculatordialog.h:
主要干两件事，声明需要的部件，声明信号和槽函数
2：calculatordialog.cpp:
主要干三件事：初始化部件、实现connect函数、实现槽函数
3：main.cpp://程序入口，创建我们定义的对话框
二：效果看了，思路有了，直接上代码
代码看着有点多，别怕，简单的很，因为太多都是重复的代码。
calculatordialog.h#ifndef CALCULATORDIALOG_H#define CALCULATORDIALOG_H#include <QDialog>//#include "ui_calculatordialog.h"#include <QPushButton>#include <QLineEdit>#include <QString>//这里采用第二种方法加载UI文件,因为是自己的部件，所以不用Uiclass calculatorDialog : public QDialog //,public Ui::calculatorDialog{Q_OBJECTpublic:explicit calculatorDialog(QWidget *parent = 0);~calculatorDialog();protected://声明需要的部件QPushButton* button_0;QPushButton* button_1;QPushButton* button_2;QPushButton* button_3;QPushButton* button_4;QPushButton* button_5;QPushButton* button_6;QPushButton* button_7;QPushButton* button_8;QPushButton* button_9;QPushButton* button_plus;QPushButton* button_minus;QPushButton* button_multiply;QPushButton* button_devide;QPushButton* button_equal;QPushButton* button_clearAll;QLineEdit* lineEdit;//声明需要的变量//第一个数，第二个数，运算结果float num1,num2,result; QString S; //用于显示在lineEdit里面的字符串//等号运算符的时候，判断是加、减、乘、除的哪一个char sign;int mark; //若点击过加减乘除，mark=2,默认是1//声明处理按钮点击信号的槽函数private slots://这种完全按照UI设计师默认的命名规则，//on_objectName_signalNamevoid on_button_0_clicked(); 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_7_clicked();void on_button_8_clicked();void on_button_9_clicked();void on_button_plus_clicked();void on_button_minus_clicked();void on_button_multiply_clicked();void on_button_devide_clicked();void on_button_equal_clicked();void on_button_clearAll_clicked();};#endif // CALCULATORDIALOG_H
calculatordialog.cpp#include "calculatordialog.h"//#include "ui_calculatordialog.h"#include <QGridLayout>calculatorDialog::calculatorDialog(QWidget *parent) :QDialog(parent){//1：初始化变量num1 = 0.0; //第一个数初始化为0num2 = 0.0; //第二个数初始化为0result = 0.0; //resutlt初始化为0S=""; //显示在编辑框的字符串初始化为空mark=1; //表示没有点击过加减乘除//初始化部件对象指针button_0= new QPushButton("0");button_1= new QPushButton("1");button_2= new QPushButton("2");button_3= new QPushButton("3");button_4= new QPushButton("4");button_5= new QPushButton("5");button_6= new QPushButton("6");button_7= new QPushButton("7");button_8= new QPushButton("8");button_9= new QPushButton("9");button_plus= new QPushButton("+");button_minus= new QPushButton("-");button_multiply= new QPushButton("*");button_devide= new QPushButton("/");button_equal= new QPushButton("=");button_clearAll= new QPushButton("c");lineEdit = new QLineEdit("C");//这里我用的网格布局，感觉比水平和垂直布局整合出来的方便很多QGridLayout *Grid = new QGridLayout;Grid->addWidget(lineEdit,1,1,1,4,Qt::Alignment());//6个参数含义：1：部件的指针；2、3：所在行和列//4、5：占用几行和几列；最后一个是对齐方式Grid->addWidget(button_0,2,1,Qt::Alignment());Grid->addWidget(button_1,2,2,Qt::Alignment());Grid->addWidget(button_2,2,3,Qt::Alignment());Grid->addWidget(button_3,2,4,Qt::Alignment());Grid->addWidget(button_4,3,1,Qt::Alignment());Grid->addWidget(button_5,3,2,Qt::Alignment());Grid->addWidget(button_6,3,3,Qt::Alignment());Grid->addWidget(button_7,3,4,Qt::Alignment());Grid->addWidget(button_8,4,1,Qt::Alignment());Grid->addWidget(button_9,4,2,Qt::Alignment());Grid->addWidget(button_plus,4,3,Qt::Alignment());Grid->addWidget(button_minus,4,4,Qt::Alignment());Grid->addWidget(button_multiply,5,1,Qt::Alignment());Grid->addWidget(button_devide,5,2,Qt::Alignment());Grid->addWidget(button_equal,5,3,Qt::Alignment());Grid->addWidget(button_clearAll,5,4,Qt::Alignment());//把Grid布局设置给当前创建的对话框对象this->setLayout(Grid);//实现连接函数connect(button_0,SIGNAL(clicked(bool)),this,SLOT(on_button_0_clicked()));connect(button_1,SIGNAL(clicked(bool)),this,SLOT(on_button_1_clicked()));connect(button_2,SIGNAL(clicked(bool)),this,SLOT(on_button_2_clicked()));connect(button_3,SIGNAL(clicked(bool)),this,SLOT(on_button_3_clicked()));connect(button_4,SIGNAL(clicked(bool)),this,SLOT(on_button_4_clicked()));connect(button_5,SIGNAL(clicked(bool)),this,SLOT(on_button_5_clicked()));connect(button_6,SIGNAL(clicked(bool)),this,SLOT(on_button_6_clicked()));connect(button_7,SIGNAL(clicked(bool)),this,SLOT(on_button_7_clicked()));connect(button_8,SIGNAL(clicked(bool)),this,SLOT(on_button_8_clicked()));connect(button_9,SIGNAL(clicked(bool)),this,SLOT(on_button_9_clicked()));connect(button_plus,SIGNAL(clicked(bool)),this,SLOT(on_button_plus_clicked()));connect(button_minus,SIGNAL(clicked(bool)),this,SLOT(on_button_minus_clicked()));connect(button_multiply,SIGNAL(clicked(bool)),this,SLOT(on_button_multiply_clicked()));connect(button_devide,SIGNAL(clicked(bool)),this,SLOT(on_button_devide_clicked()));connect(button_equal,SIGNAL(clicked(bool)),this,SLOT(on_button_equal_clicked()));connect(button_clearAll,SIGNAL(clicked(bool)),this,SLOT(on_button_clearAll_clicked()));}calculatorDialog::~calculatorDialog(){}//实现槽函数void calculatorDialog::on_button_0_clicked() //这种完全按照UI设计师默认的命名规则，on_objectName_signalName{S+="0";lineEdit->setText(S);//首先把数据设置到编辑框if(mark==1){ //判断是不是点击过：加、减、乘、除//如果没有num1=num1*10; //继续添加0，相当于乘以10}else{num2 = num2*10; }}void calculatorDialog::on_button_1_clicked(){S+="1";lineEdit->setText(S);if(mark==1){ //判断是不是点击过：加、减、乘、除//如果没有num1=num1*10+1; //继续添加6，相当于乘以10,再加1}else{num2 = num2*10+1;}}void calculatorDialog::on_button_2_clicked(){S+="2";lineEdit->setText(S);if(mark==1){ //判断是不是点击过：加、减、乘、除//如果没有num1=num1*10+2;}else{num2 = num2*10+2;}}void calculatorDialog::on_button_3_clicked(){S+="3";lineEdit->setText(S);if(mark==1){ //判断是不是点击过：加、减、乘、除//如果没有num1=num1*10+3;}else{num2 = num2*10+3;}}void calculatorDialog::on_button_4_clicked(){S+="4";lineEdit->setText(S);if(mark==1){ //判断是不是点击过：加、减、乘、除//如果没有num1=num1*10+4;}else{num2 = num2*10+4;}}void calculatorDialog::on_button_5_clicked(){S+="5";lineEdit->setText(S);if(mark==1){ //判断是不是点击过：加、减、乘、除//如果没有num1=num1*10+5;}else{num2 = num2*10+5;}}void calculatorDialog::on_button_6_clicked(){S+="6";lineEdit->setText(S);if(mark==1){ //判断是不是点击过：加、减、乘、除//如果没有num1=num1*10+6;}else{num2 = num2*10+6;}}void calculatorDialog::on_button_7_clicked(){S+="7";lineEdit->setText(S);if(mark==7){ //判断是不是点击过：加、减、乘、除//如果没有num1=num1*10+7;}else{num2 = num2*10+7;}}void calculatorDialog::on_button_8_clicked(){S+="8";lineEdit->setText(S);if(mark==1){ //判断是不是点击过：加、减、乘、除//如果没有num1=num1*10+8;}else{num2 = num2*10+8;}}void calculatorDialog::on_button_9_clicked(){S+="9";lineEdit->setText(S);if(mark==1){ //判断是不是点击过：加、减、乘、除//如果没有num1=num1*10+9;}else{num2 = num2*10+9;}}void calculatorDialog::on_button_plus_clicked(){S+="+"; //把+连接到字符串S后面sign='+'; //设置标记为+mark=2; //告诉其它数字按钮，下一个点击的数，累加到num2上lineEdit->setText(S);}void calculatorDialog::on_button_minus_clicked(){S+="-";sign='-';mark=2;lineEdit->setText(S);}void calculatorDialog::on_button_multiply_clicked(){S += "*";sign = '*';mark = 2;lineEdit->setText(S);}void calculatorDialog::on_button_devide_clicked(){S += "/";sign = '/';mark = 2;lineEdit->setText(S);}void calculatorDialog::on_button_equal_clicked(){S+="=";switch (sign) {case '+':result = num1 + num2;break;case '-':result = num1 - num2;break;case '*':result = num1 * num2;break;case '/':result = num1 / num2;break;default:break;}//S+=QString::number(result, 10); //这个函数，result必须是int类型S+=QString("%1").arg(result);//float转Qstring//S+= result+'0'; //不能这样写，result大于等于10就会报错lineEdit->setText(S);}void calculatorDialog::on_button_clearAll_clicked(){S="";lineEdit->setText(S);//sign=''; //如果bu'sh不设置为，其实也没有影响mark=1;num1 = 0.0;num2 = 0.0;result = 0.0;}
特别把这句提出来说一下： this->setLayout(Grid);
说明1：别忘了添加，这个就是把我们的布局文件添加给当前创建的对话框对象；
说明2：其实纯属的Qt设计师设计的Ui是没办法显示的，也是需要有一个parent作为依托，才能显示出来。在构造函数中会有这一句话：setupUi(this);
难免有理解不到位的地方，大家多交流学习！@_@
