QT basic hand training applet - simple calculator design (with source code, analysis)

use qt Designing a small program of calculator is very novice to practice , Here we will teach you how to realize the simplest four arithmetic calculators .

First step

1. First , I think we should figure out what functions the computer we want to have , General layout , This is a simple example of a small program , So I won't consider complex functions , There may be a lot of bug.

2. A simple calculator , Four operations should still be available ,+,-,*,/, Then another one equals , A clear

3. There should be 0-9 Ten figures , Add, subtract, multiply and divide , be equal to , Clear a total of... With a display text box at the end 17 A button

The second step

1. Now that we have figured out what controls we have , Let's first declare the controls we need in the future

    QLineEdit *le_lcd;         // Set a single line text input box 
    QPushButton *bt_num[10];   // Set up 1,2,3...9,0; Ten key positions , A separate new Out 10 Press a button , It's a silly thing for us programmers , How simple how to , So we use pointer array to realize 
    QPushButton *bt_add;        // Set up a + French key 
    QPushButton *bt_sub;        // Set up a — French key 
    QPushButton *bt_mul;        // Set a multiplication key 
    QPushButton *bt_div;        // Set a division key 
    QPushButton *bt_calc;        // Set a confirmation equal to the key 
    QPushButton *bt_chop;        // Set the key to clear one character 

The third step

1. Then we should give the declared control to new come out

 le_lcd = new QLineEdit;
    bt_chop = new QPushButton("<");

    for(int i=0; i<10; i++)
        bt_num[i] = new QPushButton(QString::number(i));

    bt_add = new QPushButton("+");
    bt_sub = new QPushButton("-");
    bt_mul = new QPushButton("*");
    bt_div = new QPushButton("/");
    bt_calc = new QPushButton("=");

Step four

Control is ready , With declaration and space , Now let's lay out these controls

To help you understand the layout , I won't use only one layout

 QHBoxLayout *hbox = new QHBoxLayout;   // Horizontal layout keys 
    hbox->addWidget(le_lcd);
    hbox->addWidget(bt_chop);
    QGridLayout *gbox = new QGridLayout;    // Grid layout keys 
    int i = 0;
    for(int y=0; y<3; y++)
        for(int x=0; x<3; x++)
            gbox->addWidget(bt_num[i++], y, x);
    gbox->addWidget(bt_num[9],3,0);
    gbox->addWidget(bt_add, 0, 3);
    gbox->addWidget(bt_sub, 1, 3);
    gbox->addWidget(bt_mul, 2, 3);
    gbox->addWidget(bt_div, 3, 1);
    gbox->addWidget(bt_calc, 3, 2, 1, 2);
    QVBoxLayout *mainbox = new QVBoxLayout;     // Vertical layout keys 
    mainbox->addLayout(hbox);
    mainbox->addLayout(gbox);
    setLayout(mainbox);   // This means , The whole is a vertical layout ,mainbox The front two layouts are installed inside 

Step five

Set slot function declaration

   public slots:
    void num_pressed(void); // Key slot function 
    void del_num(void); // Delete an input 
    void get_op(void);  // Operator key slot 
    void calculate(); // Calculation slot 

Step six

Set the signals and slots associated with the front and rear stations

for(int i=0; i<10; i++)
    connect(bt_num[i], SIGNAL(clicked(bool)), this, SLOT(num_pressed()));
    connect(bt_chop, SIGNAL(clicked(bool)), this, SLOT(del_num()));
    connect(bt_add, SIGNAL(clicked(bool)), this, SLOT(get_op()));
    connect(bt_sub, SIGNAL(clicked(bool)), this, SLOT(get_op()));
    connect(bt_mul, SIGNAL(clicked(bool)), this, SLOT(get_op()));
    connect(bt_div, SIGNAL(clicked(bool)), this, SLOT(get_op()));
    connect(bt_calc, SIGNAL(clicked(bool)), this, SLOT(calculate()));

Step seven

Specific implementation of slot function

void Widget::del_num()                        // Delete an input 
{
    QString str = le_lcd->text();
    str.chop(1);
    le_lcd->setText(str);
}
                                                    // Operator key slot 
void Widget::get_op()                                  
{
    //1.  Extract key 
    QPushButton *xbt = static_cast<QPushButton*>( sender() );
    //2.  Save symbols 
    op = xbt->text().toStdString().c_str()[0];
    //3.  Extract the first operand 
    data1 = le_lcd->text().toInt();
    le_lcd->clear();
}

void Widget::calculate()                    // Calculation slot 
{
    //0.  extract data2
    data2 = le_lcd->text().toInt();
    //1.  Calculation 
    int answer;
    switch (op) {
    case '+':
        answer = data1 + data2;
        break;
    case '-':
        answer = data1 - data2;
        break;
    case '*':
        answer = data1 * data2;
        break;
    case '/':
        answer = data1 / data2;
        break;
    default:
        break;
    }
    //2.  Show 
    le_lcd->setText(QString::number(answer));
}

void Widget::num_pressed(void)                // Operator key slot 
{
    //1.  Extract key 
    QPushButton *xbt = static_cast<QPushButton*>( sender() );
    //2.  Display the data 
    le_lcd->setText(le_lcd->text().append(xbt->text()));
}

Step eight

Go back to the header file declaration to define what we use for calculation

    char op;
    int data1;
    int data2;

Step nine

Beautify it

//5. beautify （QSS）
    this->setStyleSheet("QPushButton{"
                          "color:red;"
                        "background-color:rgb(8,189,253);"
                         "border-radius:3px;"

                         "};");

Complete code

widget.h

#ifndef WIDGET_H
#define WIDGET_H

#include <QWidget>
#include <QPushButton>
#include <QLineEdit>

class Widget : public QWidget
{
    Q_OBJECT
public slots:
    void num_pressed(void); // Key slot function 
    void del_num(void); // Delete an input 
    void get_op(void);  // Operator key slot 
    void calculate(); // Calculation slot 


public:
    Widget(QWidget *parent = 0);
    ~Widget();

    //1.  Declare the controls needed in the future 
    QLineEdit *le_lcd;
    QPushButton *bt_num[10];
    QPushButton *bt_add;
    QPushButton *bt_sub;
    QPushButton *bt_mul;
    QPushButton *bt_div;
    QPushButton *bt_calc;
    QPushButton *bt_chop;

    char op;
    int data1;
    int data2;
};

#endif // WIDGET_H

widget.cpp

#include "widget.h"
#include <QHBoxLayout>
#include <QVBoxLayout>
#include <QGridLayout>

Widget::Widget(QWidget *parent)
    : QWidget(parent)
{


    //2.  All controls new come out 
    le_lcd = new QLineEdit;
    bt_chop = new QPushButton("<");

    for(int i=0; i<10; i++)
        bt_num[i] = new QPushButton(QString::number(i));

    bt_add = new QPushButton("+");
    bt_sub = new QPushButton("-");
    bt_mul = new QPushButton("*");
    bt_div = new QPushButton("/");
    bt_calc = new QPushButton("=");

    //3.  Layout 
    QHBoxLayout *hbox = new QHBoxLayout;
    hbox->addWidget(le_lcd);
    hbox->addWidget(bt_chop);
    QGridLayout *gbox = new QGridLayout;
    int i = 0;
    for(int y=0; y<3; y++)
        for(int x=0; x<3; x++)
            gbox->addWidget(bt_num[i++], y, x);
    gbox->addWidget(bt_num[9],3,0);
    gbox->addWidget(bt_add, 0, 3);
    gbox->addWidget(bt_sub, 1, 3);
    gbox->addWidget(bt_mul, 2, 3);
    gbox->addWidget(bt_div, 3, 1);
    gbox->addWidget(bt_calc, 3, 2, 1, 2);
    QVBoxLayout *mainbox = new QVBoxLayout;
    mainbox->addLayout(hbox);
    mainbox->addLayout(gbox);
    setLayout(mainbox);


    //4.  Front and back desk Association 
    for(int i=0; i<10; i++)
    connect(bt_num[i], SIGNAL(clicked(bool)), this, SLOT(num_pressed()));
    connect(bt_chop, SIGNAL(clicked(bool)), this, SLOT(del_num()));
    connect(bt_add, SIGNAL(clicked(bool)), this, SLOT(get_op()));
    connect(bt_sub, SIGNAL(clicked(bool)), this, SLOT(get_op()));
    connect(bt_mul, SIGNAL(clicked(bool)), this, SLOT(get_op()));
    connect(bt_div, SIGNAL(clicked(bool)), this, SLOT(get_op()));
    connect(bt_calc, SIGNAL(clicked(bool)), this, SLOT(calculate()));
    //5. beautify （QSS）
   // this->setStyleSheet("QPushButton{"
     //                      "color:red;"
      //                     "background-color:rgb(8,189,253);"
       //                    "border-radius:3px;"

              //             "};");
}

void Widget::del_num()
{
    QString str = le_lcd->text();
    str.chop(1);
    le_lcd->setText(str);
}

void Widget::get_op()
{
    //1.  Extract key 
    QPushButton *xbt = static_cast<QPushButton*>( sender() );
    //2.  Save symbols 
    op = xbt->text().toStdString().c_str()[0];
    //3.  Extract the first operand 
    data1 = le_lcd->text().toInt();
    le_lcd->clear();
}

void Widget::calculate()
{
    //0.  extract data2
    data2 = le_lcd->text().toInt();
    //1.  Calculation 
    int answer;
    switch (op) {
    case '+':
        answer = data1 + data2;
        break;
    case '-':
        answer = data1 - data2;
        break;
    case '*':
        answer = data1 * data2;
        break;
    case '/':
        answer = data1 / data2;
        break;
    default:
        break;
    }
    //2.  Show 
    le_lcd->setText(QString::number(answer));
}

void Widget::num_pressed(void)
{
    //1.  Extract key 
    QPushButton *xbt = static_cast<QPushButton*>( sender() );
    //2.  Display the data 
    le_lcd->setText(le_lcd->text().append(xbt->text()));
}

Widget::~Widget()
{

}

main.cpp

#include "widget.h"
#include <QApplication>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    Widget w;
    w.show();

    return a.exec();
}

design sketch ：