Qt Tutorial 2 : C++ Calculator
The most requested next C++ app you guys asked for was a calculator, so here it is. We’ll make a C++ GUI Calculator app in one video. Along the way we’ll learn a lot! We’ll cover a topic which confuses many people which is how to setup event handling with Signals and Slots. We’ll also cover how to work with widgets in many ways, setting up an interface, stylesheets, casting, regular expressions and much more.
All of the heavily commented code follows the video below.
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Code from the Video
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DESIGN Drop QLineEdit in window -> Name it Display -> Preferred & Expanding Right Click Window -> Layout -> Layout in Grid Create QPushButtons 5 wide and 4 deep -> Preferred & Preferred 7 8 9 / M+ 4 5 6 * M- 1 2 3 + M AC 0 +/- - = Name them Button0 - Button9, Add, Subtract, Multiply, Divide, Equals, ChangeSign, Clear, MemAdd, MemClear, MemGet Line Edit Stylesheet QLineEdit { background-color: gray; border: 1px solid gray; color: #ffffff;} 10. PushButton Stylesheet QPushButton { background-color: #C0C0C0; border: 1px solid gray; border-radius: 0px; padding: 5px; } QPushButton:pressed { background-color: #A9A9A9; border: 1px solid gray; border-radius: 0px; padding: 5px; } ————— CALC.H ————— #ifndef CALC_H #define CALC_H #include <QMainWindow> // Use the standard UI namespace which is tied to the .ui file namespace Ui { class Calc; } class Calc : public QMainWindow { // Declares our class as a QObject which is the base class // for all Qt objects // QObjects handle events Q_OBJECT public: // Declare a constructor and by passing 0 we state this widget // has no parent explicit Calc(QWidget *parent = 0); ~Calc(); private: Ui::Calc *ui; // These slots are executed when a signal is // submitted (Ex. Number button is clicked) private slots : void NumPressed(); void MathButtonPressed(); void EqualButtonPressed(); void ChangeNumberSign(); }; #endif // CALC_H ————— END CALC.H ————— ————— CALC.CPP ————— #include "calc.h" #include "ui_calc.h" // Holds current value of calculation double calcVal = 0.0; // Will define if this was the last math button clicked bool divTrigger = false; bool multTrigger = false; bool addTrigger = false; bool subTrigger = false; // Constructor Calc::Calc(QWidget *parent) : // Call the QMainWindow constructor QMainWindow(parent), // Create the UI class and assign it to the ui member ui(new Ui::Calc) { // Setup the UI ui->setupUi(this); // Put 0.0 in Display ui->Display->setText(QString::number(calcVal)); // Will hold references to all the number buttons QPushButton *numButtons[10]; // Cycle through locating the buttons for(int i = 0; i < 10; ++i){ QString butName = "Button" + QString::number(i); // Get the buttons by name and add to array numButtons[i] = Calc::findChild<QPushButton *>(butName); // When the button is released call num_pressed() connect(numButtons[i], SIGNAL(released()), this, SLOT(NumPressed())); } // Connect signals and slots for math buttons connect(ui->Add, SIGNAL(released()), this, SLOT(MathButtonPressed())); connect(ui->Subtract, SIGNAL(released()), this, SLOT(MathButtonPressed())); connect(ui->Multiply, SIGNAL(released()), this, SLOT(MathButtonPressed())); connect(ui->Divide, SIGNAL(released()), this, SLOT(MathButtonPressed())); // Connect equals button connect(ui->Equals, SIGNAL(released()), this, SLOT(EqualButtonPressed())); // Connect change sign connect(ui->ChangeSign, SIGNAL(released()), this, SLOT(ChangeNumberSign())); } Calc::~Calc() { delete ui; } void Calc::NumPressed(){ // Sender returns a pointer to the button pressed QPushButton *button = (QPushButton *)sender(); // Get number on button QString butVal = button->text(); // Get the value in the display QString displayVal = ui->Display->text(); if((displayVal.toDouble() == 0) || (displayVal.toDouble() == 0.0)){ // calcVal = butVal.toDouble(); ui->Display->setText(butVal); } else { // Put the new number to the right of whats there QString newVal = displayVal + butVal; // Double version of number double dblNewVal = newVal.toDouble(); // calcVal = newVal.toDouble(); // Set value in display and allow up to 16 // digits before using exponents ui->Display->setText(QString::number(dblNewVal, 'g', 16)); } } void Calc::MathButtonPressed(){ // Cancel out previous math button clicks divTrigger = false; multTrigger = false; addTrigger = false; subTrigger = false; // Store current value in Display QString displayVal = ui->Display->text(); calcVal = displayVal.toDouble(); // Sender returns a pointer to the button pressed QPushButton *button = (QPushButton *)sender(); // Get math symbol on the button QString butVal = button->text(); if(QString::compare(butVal, "/", Qt::CaseInsensitive) == 0){ divTrigger = true; } else if(QString::compare(butVal, "*", Qt::CaseInsensitive) == 0){ multTrigger = true; } else if(QString::compare(butVal, "+", Qt::CaseInsensitive) == 0){ addTrigger = true; } else { subTrigger = true; } // Clear display ui->Display->setText(""); } void Calc::EqualButtonPressed(){ // Holds new calculation double solution = 0.0; // Get value in display QString displayVal = ui->Display->text(); double dblDisplayVal = displayVal.toDouble(); // Make sure a math button was pressed if(addTrigger || subTrigger || multTrigger || divTrigger ){ if(addTrigger){ solution = calcVal + dblDisplayVal; } else if(subTrigger){ solution = calcVal - dblDisplayVal; } else if(multTrigger){ solution = calcVal * dblDisplayVal; } else { solution = calcVal / dblDisplayVal; } } // Put solution in display ui->Display->setText(QString::number(solution)); } void Calc::ChangeNumberSign(){ // Get the value in the display QString displayVal = ui->Display->text(); // Regular expression checks if it is a number // plus sign QRegExp reg("[-+]?[0-9.]*"); // If it is a number change the sign if(reg.exactMatch(displayVal)){ double dblDisplayVal = displayVal.toDouble(); double dblDisplayValSign = -1 * dblDisplayVal; // Put solution in display ui->Display->setText(QString::number(dblDisplayValSign)); } } ————— END CALC.CPP ————— ————— MAIN.CPP ————— #include "calc.h" #include <QApplication> int main(int argc, char *argv[]) { QApplication a(argc, argv); Calc w; w.show(); return a.exec(); } ————— END MAIN.CPP ————— |
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