????if Else????

This is a discussion on ????if Else???? within the C++ Programming forums, part of the General Programming Boards category; Ok so i have to create a program that has a basic menu (i.e. apple - a, orange -o, juice ...

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    Question ????if Else????

    Ok so i have to create a program that has a basic menu (i.e. apple - a, orange -o, juice - j ) I need to create a loop that allows the customer to enter (a, o, j ) in as an option, yet at the same time rejects any other syllable thats not in the menu by letting the user know they made an invalid entry. Should I use an If else statement for this, if not can what can I use, would some one be able to show me an example and link to show more of this... Thanks for you help in advance.
    cj

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    if you are sure the user is going to enter a single character input, you can use a "switch" statement with the default case being invalid entry.

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    Registered User bradszy's Avatar
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    Code:
    #include <iostream>
    using namespace std;
    int main()
    {
    int MENUANSWER;
    MAINMENU:
    cout<<"[1] For Apple"<<endl;
    cout<<"[2] For Orange"<<endl;
    cout<<"[3] For Juice"<<endl;
    cin>>MENUANSWER;
    
    if (MENUANSWER==1)
    {
              //Apple chosen
    }
    
    else if (MENUANSWER==2)
    {
            //Orange chosen
    }
    
    else if (MENUANSWER==3)
    {
           //Juice chosen
    }
    
    else
    {
           //Invalid choice
          goto MAINMENU;
    }
    
    return 0;
    }
    Last edited by bradszy; 02-23-2008 at 06:22 PM.

  4. #4
    C++まいる!Cをこわせ! Elysia's Avatar
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    Code:
    switch(x)
    {
    	case 'a': /* Do something; */ break;
    	default: // User did not enter something acceptable
    }
    And don't use goto; use a loop instead.
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.
    For information on how to enable C++11 on your compiler, look here.
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    Registered User bradszy's Avatar
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    May I ask why not?

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    Simply put it is unsafe. There ARE many explanations of this on the board, and on google. 5 minutes of searching will get you hours of proof.

    EDIT:
    Also is this really that hard?
    Code:
    int main()
    {
    	bool quit = false;
    	char input;
    	while (!quit)
    	{
    		std::cin >> input;
    		std::ignore();
    		switch(input)
    		{
    		case 'q':
    			quit = true;
    			break;
    		default:
    			break;
    		}
    	}
    }
    I swear people are afraid of a few extra lines of code, for better readability and code security.
    Last edited by Raigne; 02-23-2008 at 10:02 PM.

  7. #7
    CSharpener vart's Avatar
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    better write your loops in the following manner:
    Code:
    while (std::cin >> input)
    {
    	std::ignore();
    	switch(input)
    	{
    	case 'q':
    		break;
    	default:
    		break;
    	}
    }
    The first 90% of a project takes 90% of the time,
    the last 10% takes the other 90% of the time.

  8. #8
    C++まいる!Cをこわせ! Elysia's Avatar
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    Quote Originally Posted by bradszy View Post
    May I ask why not?
    Mostly because it causes spaghetti code. In other words, it creates hard to read and maintainable code because goto can jump just about anywhere in the code.
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.
    For information on how to enable C++11 on your compiler, look here.
    よく聞くがいい!私は天才だからね! ^_^

  9. #9
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    There are cases where gotos can actually make the code more readable and maintainable (for example, breaking out of nested loops). However, in most other cases, it is bad.

  10. #10
    C++まいる!Cをこわせ! Elysia's Avatar
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    Indeed, but that is pretty much all that it's good for in C++. Almost.
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.
    For information on how to enable C++11 on your compiler, look here.
    よく聞くがいい!私は天才だからね! ^_^

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    Algorithm Dissector iMalc's Avatar
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    Quote Originally Posted by cyberfish View Post
    There are cases where gotos can actually make the code more readable and maintainable (for example, breaking out of nested loops).
    Such a comment is not helpful here. No beginner should ever use a goto; It's counter-productive to their necessary learning of structured programming.

    Don'y use all CAPITALS for variable names. It's ugly and harder to read, and clashes with most people's coding conventions whereby only constants and macros are all uppercase.
    My homepage
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    Quote Originally Posted by iMalc View Post
    Such a comment is not helpful here. No beginner should ever use a goto; It's counter-productive to their necessary learning of structured programming.
    But the statement was true, and it's not inconceivable that a beginner might write code that requires breaking out of a nested loop. Specific unnecessary uses of goto should be pointed out, and after finding out that 99% of them are in fact unnecessary, they'll get the idea. But I don't think they should be told that it should never be used.

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