How do I do something like if(2 variables)?

Question

I'm a beginner in Qt/C++ so while I was learning from some tutorials I wanted to make something other than the tutorial but didn't know exactly the way how.

Here is the code, I'm using curently http://pastebin.com/x612nAPV

#include "dialog.h"
#include "ui_dialog.h"
#include <QtGui>
#include <QMessageBox>
#include <QString>
 
Dialog::Dialog(QWidget *parent) :
    QDialog(parent),
    ui(new Ui::Dialog)
{
    ui->setupUi(this);
    //ui->checkBox->setChecked(true);
 
}
 
Dialog::~Dialog()
{
    delete ui;
}
 
void Dialog::on_pushButton_clicked()
{
 
    if(ui->checkBox->isChecked())
    {
        QMessageBox::information(this,"Result","Cool another Male !");
    }
 
    if(ui->checkBox_2->isChecked())
    {
        QMessageBox::information(this,"Result", "Yay a female");
    }
}

What I want to do is to make a third if() which contains 2 variables, so that in this case if none of the check boxes is checked to show a message, but I don't know how to use 2 variables in qt inside an if

like

if(2variableshere)
  {
     Do...
  }

You lack of language basics, so first of all go through some kind of C++ language book. I don't know if you noticed something in Qt "How to learn Qt": We assume that you already know C++ and will be using it for Qt development. — Kamil Klimek, Jul 25 '11 at 17:42

score 11 · Answer 1 · edited Jul 24 '11 at 12:07

To create an if statement that requires two values to be true, you combine them with the and operator, &&:

if (a && b) {
// if a and b are true

To find out if a value is false, you use the not operator, !:

if (!a) {
// if a is false

With this logic you can create this statement checking that both values are not checked.

if (!ui->checkBox_1->isChecked() && !ui->checkBox_2->isChecked()) {
// if box 1 isn't checked and box 2 isn't checked...

Related to the and operator is the or operator, ||:

if (a || b) {
// if a or b is true

We can use this to structure this condition in a different but equivalent way:

if (!(ui->checkBox_1->isChecked() || ui->checkBox_2->isChecked())) {
// if it is not the case that box 1 is checked or box 2 is checked

Rudy Velthuis · Answer 2 · 2011-07-24T12:53:59.737

I would do it like this (if I had checkboxes and one had to be chosen -- I would probably use radio buttons or a combobox with the two options instead, depending in the rest of the GUI, thus ensuring that only one of the possibilities was chosen):

void Dialog::on_pushButton_clicked()
{
    if(ui->checkBox->isChecked())
    {
        QMessageBox::information(this, "Result", "Cool another Male !");
    }
    else if(ui->checkBox_2->isChecked())
    {
        QMessageBox::information(this, "Result", "Yay a female");
    }
    else
    {
        QMessageBox::information(this, "Result", "What are you???");
    }
}

You don't need the if(2 variables) check here, since else will take care of that. But if you need something like it elsewhere, you can, of course use && and || to combine the two conditions.

As someone else said, it would be wise if you read a textbook about C or C++.

score 1 · Answer 3 · answered Jul 24 '11 at 11:47

1

void Dialog::on_pushButton_clicked()
{
    if(ui->checkBox->isChecked())
    {
        QMessageBox::information(this,"Result","Cool another Male !");
    }

    if(ui->checkBox_2->isChecked())
    {
        QMessageBox::information(this,"Result", "Yay a female");
    }

    if(!(ui->checkBox->isChecked() || ui->checkBox_2->isChecked()))
    {
        QMessageBox::infomration(this,"Result","Nothing checked.");
    }
}

answered Jul 24 '11 at 11:47

Anders Abel

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2

@ibanezz: No, && is and. || is or. I think you should read a [book on C++](http://stackoverflow.com/questions/388242/the-definitive-c-book-guide-and-list). – Armen Tsirunyan Jul 24 '11 at 11:55
1

ibanezz: no, `||` is `OR`. In C++ you could even write `and`, `or` etc. explicitly (instead of the symbols). – rubenvb Jul 24 '11 at 11:57

score 1 · Answer 4 · answered Jul 24 '11 at 11:49

1

You can use Logical operators - AND ( && ) OR ( || ) to use multiple variables in if statements. Obviously the variables are of Bool type.You can also pass functions in if statements which return bool type values..

answered Jul 24 '11 at 11:49

and in this case If I want to make: If 2 boxes are checked message "Use only one !" I'll use this: if(ui->checkBox->isChecked() && ui->checkBox_2->isChecked()) { QMessageBox::information(this,"Result","Please chose only one !"); } – ibanezz Jul 24 '11 at 11:56
This works but then after the message appears, other 2 messages appear to !? – ibanezz Jul 24 '11 at 11:58

How do I do something like if(2 variables)?

4 Answers4