QT学习笔记（四）——应用实例：计算器设置

本是古典何须时尚 2022-05-17 02:19 182阅读 0赞

# 一、界面分析： #

![70][]

# 二、相关组件介绍 #

## 2.1 QLineEdit组件 ##

作用：1. 用于接受用户输入； 2.能够获取用户输入的字符串；3.是功能性组件，需要父组件作为容器； 4.能够在父组件中进行定位

<table style="width:577px;"> 
 <tbody> 
 <tr> 
 <td style="width:574px;"> QWidget w;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;//生成QWidget对象，顶级组件 QLineEdit le(&amp;w);&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; //生成QLineEdit对象，其父组件为QWidget &nbsp; le.setAlignment(Qt::AlignRight);&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;//设置显示的字符串向右边对齐 le.move(10,10);&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; //移动到坐标（10,10）； le.resize(240, 30);&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; //设置大小width =240，heigth = 30 </td> 
 </tr> 
 </tbody> 
</table>

# 三、设计与实现 ：在程序开发前应该先进行界面设计 #

*  ## 界面设计:在程序编写前进行 ##

###          ——定义组件间的间隔 ###

Space = 10px；

###          ——定义按钮组件的大小 ###

Width = 40px，Height = 40px

###          ——定义文本框组件的大小 ###

Width = 5 \* 40px + 4 \* 10px， Height = 30px

![70 1][]

初步的程序：

#include "calculator.h"
 #include <QtWidgets/QApplication>
 #include <QWidget>
 #include <QLineEdit>
 #include <qpushbutton.h>
 
 int main(int argc, char *argv[])
 {
 	QApplication a(argc, argv);
 	QWidget *w = new QWidget; //创建父组件
 	
 	QLineEdit *le = new QLineEdit(w);//创建文本编译框
 	le -> move(10, 10);
 	le->resize(240, 30);
 
 	QPushButton *button[20] = { 0 };//创建按钮
 	const char *btnText[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[i * 5 + j] = new QPushButton(w);
 			button[i * 5 + j] -> resize(40, 40);
 			button[i * 5 + j] -> move(10 + (10 + 40) * j, 50 + (10 + 40) * i);
 			button[i * 5 + j] -> setText(btnText[i * 5 + j]);
 		}
 	}
 
 	w -> show();
 	return a.exec();
 }

结果：

![70 2][]

<table> 
 <tbody> 
 <tr> 
 <td style="width:277px;">但此时的结果有3个问题：</td> 
 <td style="width:550px;">解决办法：</td> 
 </tr> 
 <tr> 
 <td style="width:277px;">1.计算器程序不需要最大化和最小化按钮</td> 
 <td style="width:550px;"> 在创建父窗口处加上：窗口关闭函数“NULL,Qt::WindowCloseButtonHint” 即 QWidget *w = new QWidget(NULL,Qt::WindowCloseButtonHint); </td> 
 </tr> 
 <tr> 
 <td style="width:277px;">2.计算器程序的窗口应该是固定大小</td> 
 <td style="width:550px;">w-&gt;setFixedSize(w -&gt; width(), w -&gt; height());//固定窗口的大小</td> 
 </tr> 
 <tr> 
 <td style="width:277px;">3.文本框不能直接输入字符</td> 
 <td style="width:550px;">le-&gt;setReadOnly(true);//将文本框设置为只读模式</td> 
 </tr> 
 </tbody> 
</table>

对窗口做了一定限制：

#include "calculator.h"
 #include <QtWidgets/QApplication>
 #include <QWidget>
 #include <QLineEdit>
 #include <qpushbutton.h>
 
 int main(int argc, char *argv[])
 {
 	QApplication a(argc, argv);
 	QWidget *w = new QWidget(NULL,Qt::WindowCloseButtonHint); //1.创建父组件 5.加(NULL,Qt::WindowCloseButtonHint)限制窗口的最大最小化
 	
 	QLineEdit *le = new QLineEdit(w);//2.创建文本编译框
 	le -> move(10, 10);
 	le->resize(240, 30);
 	le->setReadOnly(true);//7.将文本框设置为只读模式
 
 	QPushButton *button[20] = { 0 };//3.创建按钮
 	const char *btnText[20] = //4.为按键加字符
 	{
 		"7", "8", "9", "+", "(",
 		"4", "5", "6", "-", ")",
 		"1", "2", "3", "*", "<-",
 		"0", ".", "=", "/", "C",
 	};
 
 	for (int i = 0; i < 4; i++) //3.创建按钮
 	{
 		for (int j = 0; j < 5; j++)
 		{
 			button[i * 5 + j] = new QPushButton(w);
 			button[i * 5 + j] -> resize(40, 40);
 			button[i * 5 + j] -> move(10 + (10 + 40) * j, 50 + (10 + 40) * i);
 			button[i * 5 + j] -> setText(btnText[i * 5 + j]);
 		}
 	}
 
 	w -> show();
 	w->setFixedSize(w -> width(), w -> height());//6.固定窗口的大小
 	return a.exec();
 }

结果：

![70 3][]

# 小结： #

![70 4][]

# 四、按键在屏幕上显示 #

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# 五、计算器四则运算的实现 #

<table style="width:500px;"> 
 <tbody> 
 <tr> 
 <td>中缀表达式</td> 
 <td>后缀表达式</td> 
 </tr> 
 <tr> 
 <td>5+3</td> 
 <td>5 3 +</td> 
 </tr> 
 <tr> 
 <td>1+2*3</td> 
 <td>1 2 3 * +</td> 
 </tr> 
 <tr> 
 <td>9+（3-1）*5</td> 
 <td>9 3 1 - 5 * +</td> 
 </tr> 
 </tbody> 
</table>

我们习惯的数学表达式叫中缀表达式，还有一种将运算符放在数字后面的叫后缀表达式。后缀表达式更适合机器

[70]: /images/20220517/592ee3557ee8404090656634e8ccf455.png
[70 1]: /images/20220517/94bd3a6043794c318ad847966b024ccb.png
[70 2]: /images/20220517/76ec74fb058f44ddb15c129756f5959d.png
[70 3]: /images/20220517/2e990ff8b47e4ca9a95e06fd9699a647.png
[70 4]: /images/20220517/64a3af3651524689828a6fa9d7e6c443.png
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