Problem with simple program

This is a discussion on Problem with simple program within the C++ Programming forums, part of the General Programming Boards category; Hi guys, I was wondering if you can help me with that. I wrote a simple program (I have just ...

  1. #1
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    Problem with simple program

    Hi guys,
    I was wondering if you can help me with that. I wrote a simple program (I have just started learning C++) but it doesn't work as expected. Here is the program and I will explain what I would like to do and what happens when I execue it:

    Code:
    //seventh first
    #include <iostream>
    using std::cout;
    using std::cin;
    using std::endl;
    
    class Maths
    {
    public:
    void enterInstructions( int instructions )
    	{
    	cout <<"I want to do a: \nAddition\nSubtraction\nType your choice here: "<< instructions << endl;
    	}
    void conditions(int instructions)
    	{
    	int result;
    	int Addition;
    	int Subtraction;
    	if ( instructions == Addition )
    	cout << "Enter the right number: 9+3= "<< endl;
    	cin >> result;
    	if ( result == 12 )
    	cout << "Well done, you're a star!";
    	if ( result != 12 )
    	cout << "Sorry, wrong answer!";
    	if ( result < 12 )
    	cout << "Sorry, wrong answer!";
    	if ( result > 12 )
    	cout << "Sorry, wrong answer!";
    
    	if ( instructions == Subtraction )
    	cout << "Enter the right number: 9-3= ";
    	cin.ignore ( 80, '\n' );
    	cin >> result;
    	
    	if ( result == 6 )
    	cout << "Well done, you're a star!";
    	if ( result != 6 )
    	cout << "Sorry, wrong answer!";
    	if ( result < 6 )
    	cout << "Sorry, wrong answer!";
    	if ( result > 6 )
    	cout << "Sorry, wrong answer!";
    	}
    };
    
    int main()
    {
    int myInstructions;
    Maths operations;
    cout << "What do you want to do?\n";
    
    operations.enterInstructions( myInstructions );
    cin >> myInstructions;
    operations.conditions( myInstructions );
    
    
    return 0;
    }
    Basically I would like this program to let me choose whether I want to guess the result of an addition or a subtraction. Once I made my choice the program should display the addition/subtraction and I should be able to guess the result. If I guess it right the "Well done, you're a star!" messages appear, if not the "Sorry, wrong answer!" message comes up instead.
    Now here is what happens. I use Visual C++ as a compiler and when I compile the program it does it with no errors but 3 warning as below:


    --------------------Configuration: 10 - Win32 Debug--------------------
    Compiling...
    10th.cpp
    Z:\example\10\10th.cpp(53) : warning C4700: local variable 'myInstructions' used without having been initialized
    Z:\example\10\10th.cpp(19) : warning C4700: local variable 'Addition' used without having been initialized
    Z:\example\10\10th.cpp(31) : warning C4700: local variable 'Subtraction' used without having been initialized
    Linking...

    10.exe - 0 error(s), 3 warning(s)

    When I execute the program from the compiler this is what the terminal returns:

    What do you want to do?
    I want to do a:
    Addition
    Subtraction
    Type your choice here: -858993460

    I can't explain the above number...
    then if I type Subtraction, here's what the terminal display:

    What do you want to do?
    I want to do a:
    Addition
    Subtraction
    Type your choice here: -858993460
    Subtraction
    Enter the right number: 9+3=
    Sorry, wrong answer!Sorry, wrong answer!Enter the right number: 9-3= Sorry, wron
    g answer!Sorry, wrong answer!Press any key to continue

    So basically the addition comes up even if I chose subtraction, but what's worse is that it doesn't let me type the result of the operation, it displays straight away "Sorry wrong answer". I can't understand what I have done wrong...could anybody suggest anything?
    Thanks

  2. #2
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    Mar 2009
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    You are using variables without initializing them to anything.

    For example, what exactly do you expect Addition to be here? You haven't assigned it a value yet, so how can you use it to compare it against anything?
    Code:
    int Addition;
    	int Subtraction;
    	if ( instructions == Addition )

  3. #3
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    Thanks for your reply.
    Uhm, I didn't know I had to initialize them. The thing is I would like the condition to be largely this: if the parameter instructions = addition then display "Enter the right number: 9+3= ", if instructions = subtraction then display "Enter the right number: 9-3= ". Now, if I need to initialize the "Addition", "Subtraction", "Results" and "myInstructions" - in main - variables, what initial value am I suppose to give them? I have written other programs without the need of initializing a variable, so I am a bit confused on this...

  4. #4
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    When I say initialize, I meant that you should assign the variable a value before you use it.

    For example, you have a lot of code that does this:
    Code:
    int number;
    cout << number << endl;
    What is cout going to print here? Who knows, it's going to be a random number that is currently stored at the memory location that the variable number occupies.

  5. #5
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    Ok I see what you mean in your example. But if I add
    Code:
    int number;
    cin >> number;
    cout << number << endl;
    then I don't need to initialize the variable anymore, because it will take the value from what the user will type in...or am I wrong?

    In my case, I understand that those variables need to be initialised but I can't understand what value they should have if I want the program to execute properly. If I give them an initial value, it will not change during the program execution, because "addition", "subtraction" and "myInstructions" don't actually take any value. So, maybe I got things wrong, sorry. If I want a user to be able to make a choice between addition and subtraction, and the program to be able to present him with respectively "Enter the right number: 9+3= " or "Enter the right number: 9-3= " depending on his choice then I shouldn't use that code?

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