Switch Statements

This is a discussion on Switch Statements within the C++ Programming forums, part of the General Programming Boards category; Hi, I'm a beginner and lost on my assignment already--stuck on the switch statements. I've looked at the tutorials already ...

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    Switch Statements

    Hi,

    I'm a beginner and lost on my assignment already--stuck on the switch statements. I've looked at the tutorials already but I still can't find my answer so I'm here. My assignment is a quiz so I can't really ask specific questions. I'm just confused about some parts. I know that in the if/else statement, you can have eqns like y=x+3 and then enter in an x value in the if statement to calculate what y is. I've been trying to do the same for the switch statement but I can't.

    Also, I want to add all the cases together, like case 1 = case 1+case2+case3, then case 2 = case 2 +case3

    with the cases being numbers of course. any help is appreciated, thanks.

  2. #2
    C++ Witch laserlight's Avatar
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    I've looked at the tutorials already
    As in Lesson 5: switch case?

    I know that in the if/else statement, you can have eqns like y=x+3 and then enter in an x value in the if statement to calculate what y is. I've been trying to do the same for the switch statement but I can't.
    You might want to give an example of what you mean in terms of if/else.

    Also, I want to add all the cases together, like case 1 = case 1+case2+case3, then case 2 = case 2 +case3
    What do you mean by "add"? One feature (or 'misfeature', depending on your point of view) is that of 'fall-through', as in once a case is reached, control moves to the following case in the absence of say, a break.
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
    I get maybe two dozen requests for help with some sort of programming or design problem every day. Most have more sense than to send me hundreds of lines of code. If they do, I ask them to find the smallest example that exhibits the problem and send me that. Mostly, they then find the error themselves. "Finding the smallest program that demonstrates the error" is a powerful debugging tool.
    Look up a C++ Reference and learn How To Ask Questions The Smart Way

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    I'm not clear on your first question. If I understand the second one, you can do
    Code:
    switch (n) {
    case 1:
    case 2:
    case 3:
      // do something
      break;
    case 4:
    case 5:
      // do something else
      break;
    }
    You're just using switch's fallthrough.

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    Yes, tutorial 5.

    Example:

    if(x=5)
    y=x+3;
    printf("y = %f\n",y);

    I don't know how to insert equations into the switch statement. Is that even allowed in the switch statement? To calculate an eqn?

    I tried the the fall through one (I did it without break; ), but it didn't add the numbers together. All it did was list them together.

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    I think you want "x == 5" (one equals is assignment).

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    oh yes. bad mistake.

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    C++ Witch laserlight's Avatar
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    I presume you actually mean:
    Code:
    if (x == 5)
    {
        y = x + 3;
        printf("y = %f\n", y);
    }
    In a switch, this might be:
    Code:
    switch (x)
    {
    case 5:
        y = x + 3;
        printf("y = %f\n", y);
        break;
    }
    Or, if you are declaring a variable within a case:
    Code:
    switch (x)
    {
    case 5:
        {
            double y = x + 3;
            printf("y = %f\n", y);
        }
        break;
    }
    I note that in C++, we usually use output streams like std::cout instead of C-style output functions like printf().

    I tried the the fall through one (I did it without break; ), but it didn't add the numbers together. All it did was list them together.
    Add what numbers together?
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
    I get maybe two dozen requests for help with some sort of programming or design problem every day. Most have more sense than to send me hundreds of lines of code. If they do, I ask them to find the smallest example that exhibits the problem and send me that. Mostly, they then find the error themselves. "Finding the smallest program that demonstrates the error" is a powerful debugging tool.
    Look up a C++ Reference and learn How To Ask Questions The Smart Way

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    I've only seen printf(), never std::cout, have no idea why.

    Add the results from each case. Like if I calculate:

    y (case 1) to be = 5
    y (case 2) = 4
    y (case 3) = 3

    Then when I do the switch statement and call on case 1, without using break, it would give me y = 12. But instead, all it did was give me something like:

    y = 5
    y = 4
    y = 3

    rather than y = 12.

  9. #9
    C++ Witch laserlight's Avatar
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    Perhaps you are looking for something like this:
    Code:
    int y = 0;
    switch (x)
    {
    case 1: y += 5;
    case 2: y += 4;
    case 3: y += 3;
    }
    But honestly, if you are not cautious and prudent in your use of fall through it can get more confusing than it is worth.
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
    I get maybe two dozen requests for help with some sort of programming or design problem every day. Most have more sense than to send me hundreds of lines of code. If they do, I ask them to find the smallest example that exhibits the problem and send me that. Mostly, they then find the error themselves. "Finding the smallest program that demonstrates the error" is a powerful debugging tool.
    Look up a C++ Reference and learn How To Ask Questions The Smart Way

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    > I've only seen printf(), never std::cout, have no idea why.
    Well, this is the C++ forum, and std::cout is the C++ counterpart to printf() (you can still use printf() but it's discouraged).
    I think what you're trying to do is to add something to y in each case. In that case, you would want something like "y += 5;" in case 1, "y += 4;" in case 2, etc. You also need to initialize y to 0 before the switch statement.

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    Sorry but I have another question. If I use y in the switch statement, then I'd identify it in the beginning as:

    double y;

    right?

    Because for some reason, all my ys are zeros now.

  12. #12
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    Because for some reason, all my ys are zeros now.
    What is your current code?
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
    I get maybe two dozen requests for help with some sort of programming or design problem every day. Most have more sense than to send me hundreds of lines of code. If they do, I ask them to find the smallest example that exhibits the problem and send me that. Mostly, they then find the error themselves. "Finding the smallest program that demonstrates the error" is a powerful debugging tool.
    Look up a C++ Reference and learn How To Ask Questions The Smart Way

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    Nvm, got it. Thanks for the help.
    Last edited by lazyturtle; 05-02-2007 at 03:28 AM.

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