I need to write a program in QT4 that converts the value entered by the user to Celsius or to Fahrenheit

The temperatue.cpp:

I need to write a program that converts celcius to fahrenheit and vice versa

the temperature.cpp is:

#include "temperature.h"
//constructor
Temperature::Temperature() {
//{initializes and places widgets using a layout
setWindowTitle("Celcius to Fahrenheit Converter");
QGridLayout* layout = new QGridLayout;
QLabel* inputRequest = new QLabel("Enter the temperature ");
tempEntry = new QLineEdit;
tempEntry->setMaxLength(20);
tempEntry->setAlignment(Qt::AlignRight);
QPushButton* convertC = new QPushButton("C_To_F");
QPushButton* convertF = new QPushButton("F_To_C");
QLabel* labelC = new QLabel("Celcius ");
resultC = new QLCDNumber;
resultC->setSegmentStyle(QLCDNumber::Flat);
resultC->setDigitCount(4);
QLabel* labelF = new QLabel("Fahrenheit ");
resultF = new QLCDNumber;
resultF->setSegmentStyle(QLCDNumber::Flat);
resultF->setDigitCount(4);
QPushButton* clear = new QPushButton("Clear All");
layout->addWidget(inputRequest, 0,0);
layout->addWidget(tempEntry, 0,1);
layout->addWidget(convertC, 0,2);
layout->addWidget(convertF, 1,2);
layout->addWidget(new QLabel, 1, 0); //for spacing
layout->addWidget(labelC,2,0);
layout->addWidget(resultC,2,1);
layout->addWidget(labelF,3,0);
layout->addWidget(resultF,3,1);
layout->addWidget(clear, 4,1);
setLayout(layout);
//}
//{ connect signals and slots
connect(convertC, SIGNAL(clicked()), this, SLOT(calculateC()));
connect(convertF, SIGNAL(clicked()), this, SLOT(calculateF()));
connect(clear, SIGNAL(clicked()), this, SLOT(clearFields()));
//}
}
// display the Celcius equivalent of the int
void Temperature::calculateC() {
int answer=0;
double ctemp;

QString iStr = tempEntry->text();
bool ok;
int i = iStr.toInt(&ok);
if (!ok) {
error = new QErrorMessage(this);
error->showMessage("Please enter a valid integer");
}
resultC->display(i);
}

// display the Fahrenheit equivalent of the int
void Temperature::calculateF() {
int answer=0;
double ftemp;
QString iStr = tempEntry->text();
bool ok;
int i = iStr.toInt(&ok);
if (!ok) {
error = new QErrorMessage(this);
error->showMessage("Please enter a valid integer");
}
resultF->display(i);
}

//clear widgets
void Temperature::clearFields(){
tempEntry->clear();
resultC->display(0);
resultF->display(0);
}

How do I add the conversion calculations?

Here are the formulae for converting between Fahrenheit and Celsius:

Celsius = (5.0 / 9.0) * (Fahrenheit - 32)
Fahrenheit = (9.0 / 5.0) * Celsius + 32

Once you have the values for Celsius or Fahrenheit, just plug in the formula at the appropriate place and display the result.