connecting a signal of widget in a plasmoid

I am new to Qt and am trying to connect the cilicked signal o a push button with a function hile writing a plasmoid. I am trying to use an external function as a public with Plasma::PushButton type object so that I can use it to connect it with the clicked signal? With gtk it was as simple as on_...._clicked do this but isnt there a simple way in qt, where we can do away with the need to use slots?

#include "plasma-tutorial1.h"
#include<string.h>
#include <stdlib.h>
#include <QGraphicsLinearLayout>
#include <QPainter>
#include <QFontMetrics>
#include <QSizeF>
#include <QTextEdit>
#include <plasma/svg.h>
#include <plasma/theme.h>
#include <plasma/widgets/lineedit.h>
#include <plasma/widgets/pushbutton.h>
#include <plasma/widgets/textedit.h> 
//PlasmaTutorial1 mainf;

themainfunction(int choice,Plasma::LineEdit *m_lineEdit,
Plasma::TextEdit *m_displaytext)
{
char buffer[100];
const char *inp=(const char *)malloc(sizeof(char)*100);
QString input;
input=m_lineEdit->text();
QByteArray byteArray = input.toUtf8();
inp = byteArray.constData();
char *expression;
expression=(char *)malloc(sizeof(char)*100);
strcpy(expression,"sudo apt-");

switch(choice)
{
case 1:{
        strcat(expression,"get install ");
        strcat(expression,inp);
        break;
      };
case 2:{
        strcat(expression,"get remove ");
        strcat(expression,inp);
        break;
      };
case 3:{
        strcat(expression,"cache search ");
        strcat(expression,inp);
        break;
      };
};
/*
FILE* in;
FILE* ptr=fopen("new.txt","w");
FILE *popen();
if(!(in = popen("cal","r")))
    {return;}

    while(fgets(buffer, 100, in) != NULL) {
*/
m_displaytext->append("yeah!");
//    fprintf(ptr,"%s",buffer);

            //}
//pclose(in);
//fclose(ptr);
}
PlasmaTutorial1::PlasmaTutorial1(QObject *parent, const QVariantList &args)
    : Plasma::Applet(parent, args),
    m_svg(this),
    m_icon("document")
{
    m_svg.setImagePath("widgets/background");
    // this will get us the standard applet background, for free!
    setBackgroundHints(DefaultBackground);
    resize(200, 200);
}


PlasmaTutorial1::~PlasmaTutorial1()
{
    if (hasFailedToLaunch()) {
        // Do some cleanup here
    } else {
        // Save settings
    }
}

void PlasmaTutorial1::init()
{

  /*  // A small demonstration of the setFailedToLaunch function
    if (m_icon.isNull()) {
        setFailedToLaunch(true, "No world to say hello");
    }*/
Counter rt;
    QGraphicsLinearLayout *layout = new QGraphicsLinearLayout(this);
  layout->setOrientation(Qt::Vertical); //so widgets will be stacked up/down

  m_lineEdit = new Plasma::LineEdit(this);
  m_lineEdit->setText("Enter the package name here");

  m_displaytext = new Plasma::TextEdit(this);
  m_displaytext->setText("Terminal");

  m_installButton = new Plasma::PushButton(this);
  m_installButton->setText("Install");
  connect(m_installButton, SIGNAL(clicked()),&rt,SLOT(themainfunction(1,m_lineEdit,m_displaytext)));

  m_removeButton = new Plasma::PushButton(this);
  m_removeButton->setText("Remove");
  // m_removeButton->clicked()

  connect(m_removeButton, SIGNAL(clicked()),&rt,SLOT(themainfunction(2,m_lineEdit,m_displaytext)));

  m_searchButton = new Plasma::PushButton(this);
  m_searchButton->setText("Search");
  connect(m_searchButton, SIGNAL(clicked()),&rt,SLOT(themainfunction(3,m_lineEdit,m_displaytext)));


  layout->addItem(m_lineEdit);
  layout->addItem(m_installButton);
  layout->addItem(m_removeButton);
  layout->addItem(m_searchButton);
  layout->addItem(m_displaytext);   
  m_displaytext->append("yo baby!");    
} 

/* 
void PlasmaTutorial1::paintInterface(QPainter *p,
        const QStyleOptionGraphicsItem *option, const QRect &contentsRect)
{
    p->setRenderHint(QPainter::SmoothPixmapTransform);
    p->setRenderHint(QPainter::Antialiasing);

    // Now we draw the applet, starting with our svg
    m_svg.resize((int)contentsRect.width(), (int)contentsRect.height());
    m_svg.paint(p, (int)contentsRect.left(), (int)contentsRect.top());

    // We place the icon and text
    p->drawPixmap(7, 0, m_icon.pixmap((int)contentsRect.width(),(int)contentsRect.width()-14));
    p->save();
    p->setPen(Qt::white);
    p->drawText(contentsRect,
                Qt::AlignBottom | Qt::AlignHCenter,
                "Hello Plasmoid!");
    p->restore();
}
 */
// This is the command that links your applet to the .desktop file
K_EXPORT_PLASMA_APPLET(tutorial1, PlasmaTutorial1)

#include "plasma-tutorial1.moc"

say i want to connect themainfunction() upon clicked signal of install button . how do i do it? how can I derive a class in plasma?

i got where was i missing out. We cannot pass objects as arguments in slot functions. Now it is running smooth. thanx for all your replies.