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  4. problems on using the if and else statement and updating the data.

problems on using the if and else statement and updating the data.

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c++ qtupdateif and else
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  • M Mr.Nobody645
    25 Jun 2020, 10:18

    im appreciate for both of you on helping me in the if and else part. However, when i try to checked AddOn1 and AddOn2, i got my price 2.50 instead of 3.70.

    J Online
    J Online
    J.Hilk
    Moderators
    wrote on 25 Jun 2020, 10:20 last edited by
    #6

    @Mr-Nobody645 said in problems on using the if and else statement and updating the data.:

    im appreciate for both of you on helping me in the if and else part. However, when i try to checked AddOn1 and AddOn2, i got my price 2.50 instead of 3.70.

    obviously, as

    if (ui-> AddOn1 -> isChecked()){
    price = 2.50;
    }

    comes before everything else and its true so the rest of the checks is not executed


    Be aware of the Qt Code of Conduct, when posting : https://forum.qt.io/topic/113070/qt-code-of-conduct


    Q: What's that?
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    • M Mr.Nobody645
      25 Jun 2020, 10:18

      im appreciate for both of you on helping me in the if and else part. However, when i try to checked AddOn1 and AddOn2, i got my price 2.50 instead of 3.70.

      J Offline
      J Offline
      JonB
      wrote on 25 Jun 2020, 11:03 last edited by JonB
      #7

      @Mr-Nobody645 said in problems on using the if and else statement and updating the data.:

      However, when i try to checked AddOn1 and AddOn2, i got my price 2.50 instead of 3.70.

      That's why I wrote earlier:

      In which case you'll need to test that [if (ui-> AddOn1-> isChecked() && ui-> AddOn2-> isChecked())] before testing ui-> AddOn1-> isChecked() or ui-> AddOn2-> isChecked() individually.

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      • S sierdzio
        25 Jun 2020, 10:07

        Do you actually want to ask some question here? What is your problem?

        Do you mean to ask how to check multiple values at once in an if statement?

        ui-> (AddOn1 + AddOn2 + AddOn3) -> isChecked()

        Here is something which should work:

        if (ui->AddOn1->isChecked() && ui->AddOn2->isChecked() && ui->AddOn3->isChecked())
        

        But for sake of readability and maintenance (and, to some degree, performance), I'd suggest to get state first, and check later:

        const bool isAddOn1 = ui->AddOn1->isChecked();
        const bool isAddOn2 = ui->AddOn2->isChecked();
        const bool isAddOn3 = ui->AddOn3->isChecked();
        if (isAddOn1 && isAddOn2 && isAddOn3)
        // ...
        

        All modernt compilers also understand and as a synonym to && so you can do:

        if (isAddOn1 and isAddOn2 and isAddOn3)
        
        J Offline
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        JonB
        wrote on 25 Jun 2020, 11:07 last edited by JonB
        #8

        @sierdzio said in problems on using the if and else statement and updating the data.:

        All modernt compilers also understand and as a synonym to && so you can do:

        I am speechless! Apart from the fact that I have never heard of this (old time C/C++ programmer, now returned to new C++). And apart from the fact that introducing and as a language keyword would potentially break one million old C/C++ programs which could have used and as a variable?

        You are obviously more expert than I, but do you want to recommend this to a newbie? I have never noticed and used in a C++ program, if OP is to produce standard code, and recognize others' code, would you not recommend sticking with &&?

        J 1 Reply Last reply 25 Jun 2020, 11:18
        0
        • J JonB
          25 Jun 2020, 11:07

          @sierdzio said in problems on using the if and else statement and updating the data.:

          All modernt compilers also understand and as a synonym to && so you can do:

          I am speechless! Apart from the fact that I have never heard of this (old time C/C++ programmer, now returned to new C++). And apart from the fact that introducing and as a language keyword would potentially break one million old C/C++ programs which could have used and as a variable?

          You are obviously more expert than I, but do you want to recommend this to a newbie? I have never noticed and used in a C++ program, if OP is to produce standard code, and recognize others' code, would you not recommend sticking with &&?

          J Online
          J Online
          J.Hilk
          Moderators
          wrote on 25 Jun 2020, 11:18 last edited by
          #9

          @JonB apparently part of the standard since c++98
          https://en.cppreference.com/w/cpp/keyword/and


          Be aware of the Qt Code of Conduct, when posting : https://forum.qt.io/topic/113070/qt-code-of-conduct


          Q: What's that?
          A: It's blue light.
          Q: What does it do?
          A: It turns blue.

          J 1 Reply Last reply 25 Jun 2020, 11:29
          2
          • J J.Hilk
            25 Jun 2020, 11:18

            @JonB apparently part of the standard since c++98
            https://en.cppreference.com/w/cpp/keyword/and

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            J Offline
            JonB
            wrote on 25 Jun 2020, 11:29 last edited by JonB
            #10

            @J-Hilk , @sierdzio
            Absolutely shocking! I see from https://en.cppreference.com/w/cpp/language/operator_alternative that there are actually 11 new reserved words for operators. Including not, and even the string compl, which I might have used as variables and would break upgrading to C++ '98.

            Thinking aloud, I believe all C operators were symbols and not words, part of the charm (for right or for wrong) of the language.

            With all due respect to @sierdzio's comment, which I accept & respect, I have still never seen a piece of C++ code using any of these.... [And hence would caution a beginner against adopting these.]

            [C++ looks like it's trying to be a Python-wannabe ;-) ]

            J 1 Reply Last reply 25 Jun 2020, 11:30
            1
            • J JonB
              25 Jun 2020, 11:29

              @J-Hilk , @sierdzio
              Absolutely shocking! I see from https://en.cppreference.com/w/cpp/language/operator_alternative that there are actually 11 new reserved words for operators. Including not, and even the string compl, which I might have used as variables and would break upgrading to C++ '98.

              Thinking aloud, I believe all C operators were symbols and not words, part of the charm (for right or for wrong) of the language.

              With all due respect to @sierdzio's comment, which I accept & respect, I have still never seen a piece of C++ code using any of these.... [And hence would caution a beginner against adopting these.]

              [C++ looks like it's trying to be a Python-wannabe ;-) ]

              J Online
              J Online
              jsulm
              Lifetime Qt Champion
              wrote on 25 Jun 2020, 11:30 last edited by
              #11

              @JonB said in problems on using the if and else statement and updating the data.:

              I have still never seen a piece of C++ code using any of these

              Me neither :-)

              https://forum.qt.io/topic/113070/qt-code-of-conduct

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              • S Offline
                S Offline
                sierdzio
                Moderators
                wrote on 25 Jun 2020, 11:33 last edited by
                #12

                I have seen it but very, very rarely.

                And hence would caution a beginner against adopting these

                I'm split on this :D One one hand, && is clearly, vastly, totally the established and well-known convention practically everywhere. So using it is definitely a good idea.

                But on the other hand, and is more readable and convenient. So it is also a good idea.

                (Z(:^

                J 1 Reply Last reply 25 Jun 2020, 11:36
                1
                • S sierdzio
                  25 Jun 2020, 11:33

                  I have seen it but very, very rarely.

                  And hence would caution a beginner against adopting these

                  I'm split on this :D One one hand, && is clearly, vastly, totally the established and well-known convention practically everywhere. So using it is definitely a good idea.

                  But on the other hand, and is more readable and convenient. So it is also a good idea.

                  J Offline
                  J Offline
                  JonB
                  wrote on 25 Jun 2020, 11:36 last edited by JonB
                  #13

                  @sierdzio said in problems on using the if and else statement and updating the data.:

                  But on the other hand, and is more readable and convenient.

                  In Pascal or Python, yes. When scanning C/C++ I expect to see all operators as symbols (and not some but not others) Next C++ will be offering begin/end for {/}! [Some people used to do all this words-for-symbols via C #defines.] I give up on the modern world, it's all going to pot... ;-)

                  J 1 Reply Last reply 25 Jun 2020, 11:41
                  1
                  • J JonB
                    25 Jun 2020, 11:36

                    @sierdzio said in problems on using the if and else statement and updating the data.:

                    But on the other hand, and is more readable and convenient.

                    In Pascal or Python, yes. When scanning C/C++ I expect to see all operators as symbols (and not some but not others) Next C++ will be offering begin/end for {/}! [Some people used to do all this words-for-symbols via C #defines.] I give up on the modern world, it's all going to pot... ;-)

                    J Online
                    J Online
                    J.Hilk
                    Moderators
                    wrote on 25 Jun 2020, 11:41 last edited by
                    #14

                    @JonB said in problems on using the if and else statement and updating the data.:

                    Next C++ will be offering begin/end for {/}!

                    you can use

                    {	??<
                    }	??>
                    [	??(
                    ]	??)
                    #	??=
                    \	??/
                    ^	??'
                    |	??!
                    ~	??-
                    

                    but that was removed in c++17, :)


                    Be aware of the Qt Code of Conduct, when posting : https://forum.qt.io/topic/113070/qt-code-of-conduct


                    Q: What's that?
                    A: It's blue light.
                    Q: What does it do?
                    A: It turns blue.

                    J 1 Reply Last reply 25 Jun 2020, 11:48
                    1
                    • J J.Hilk
                      25 Jun 2020, 11:41

                      @JonB said in problems on using the if and else statement and updating the data.:

                      Next C++ will be offering begin/end for {/}!

                      you can use

                      {	??<
                      }	??>
                      [	??(
                      ]	??)
                      #	??=
                      \	??/
                      ^	??'
                      |	??!
                      ~	??-
                      

                      but that was removed in c++17, :)

                      J Offline
                      J Offline
                      JonB
                      wrote on 25 Jun 2020, 11:48 last edited by JonB
                      #15

                      @J-Hilk

                      but that was removed in c++17, :)

                      Even better --- you start using new language constructs and then they remove them so that your code gets broken!

                      FWIW, I note from https://en.cppreference.com/w/cpp/language/operator_alternative

                      There are alternative spellings for several operators and other tokens that use non-ISO646 characters.

                      So the motivation never was "clarity", it's to do with people having funny keyboards....

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                      1
                      • SGaistS Offline
                        SGaistS Offline
                        SGaist
                        Lifetime Qt Champion
                        wrote on 25 Jun 2020, 19:29 last edited by
                        #16

                        @JonB said in problems on using the if and else statement and updating the data.:

                        funny keyboards

                        The hardware is innocent ;-P

                        Interested in AI ? www.idiap.ch
                        Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

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                        0
                        • Kent-DorfmanK Offline
                          Kent-DorfmanK Offline
                          Kent-Dorfman
                          wrote on 25 Jun 2020, 22:51 last edited by
                          #17

                          whats next, espousing the virtues of trigraphs?

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                          0
                          • 1 Offline
                            1 Offline
                            1Manui1
                            wrote on 16 Dec 2021, 18:50 last edited by
                            #18

                            How did you do it now?

                            1 Reply Last reply
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