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Thread: Build this simple progam according to earlier standards

  1. #1
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    Build this simple progam according to earlier standards

    I am new to C++ and have learned that when I build a program and I want to learn how, it is best to build each program according to the same standard.

    In my programs I want to have a function protocol before the main section and a function definition after the main section.

    Now I would like to build a program that takes 2 integers and switches them, integer A becomes integer B and the other way around. Simple.

    What I have now is this:

    Code:
    #include <iostream>
    using namespace std;
    
    int ChangeInteger(int, int, int); // protocol
    
    int main()
    {
    int IntegerA;
    int IntegerB;
    int IntegerTemp;
    
    cout << "Type 1st integer: ";
    cin  >> IntegerA;
    
    cout << "Type 2nd integer: ";
    cin  >> IntegerB;
    
    IntegerTemp = 5;
    
    cout << "The value of IntegerA is " << ChangeInteger(IntegerA, IntegerB, IntegerTemp) << endl;
    
    system ("pause");
    
    return 0;
    }
    
    int ChangeInteger (int Integer_A, int Integer_B, int Integer_Temp) // definition
    
    {
    int result = Integer_B; 
    return result;
    }
    
    int ChangeInteger2(int, int, int); // protocol
    
    {
    int IntegerA;
    int IntegerB;
    int IntegerTemp;
    
    cout << "The value of IntegerB is " << ChangeInteger2(IntegerA, IntegerB, IntegerTemp) << endl;
    
    int ChangeInteger2 (int Integer_A, int Integer_B, int Integer_Temp) // definition
    
    int result2 = Integer_A;
    return result2;
    }
    This is not working, it is giving me the following error on the "{" sign that comes below the line with the "int ChangeInteger2 (int Integer_A, int Integer_B, int Integer_Temp)" function definition.

    error C2447: '{' : missing function header (old-style formal list?)

    By the way, is it good practice to have a protocol and a definition in each program?

  2. #2
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    Re: Build this simple progam according to earlier standards

    It is good to use code tags, but better to indent your code so that the code tags become effective.

    This is not working, it is giving me the following error on the "{" sign that comes below the line with the "int ChangeInteger2 (int Integer_A, int Integer_B, int Integer_Temp)" function definition.
    ChangeInteger2 looks problematic in that the line with the "definition" comment is out of place. It looks as if you are trying to redefine the function in its body.

    By the way, is it good practice to have a protocol and a definition in each program?
    I think you mean prototype and definition. I would say that this is usually good practice. The prototypes (and class declarations) would go in header files, and the function and class implementation into the source files.

    What you are trying to do is to swap two variables. Typically we do use a temporary variable to perform the swap, but this variable will be local to the swap function. Instead of returning a value (you cannot really swap just by returning a value), we would pass the variables as references. An example (implementation not shown) would be:
    Code:
    void swap(int& a, int& b)
    {
        // Create a temporary int.
        // Use the temporary to perform the swap.
    }
    Note that the standard library provides a generic std::swap with the same function signature, so my example might not work since you are using namespace std.
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  3. #3
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    Re: Build this simple progam according to earlier standards

    Looks like LaserLight caught most of the problems with your code.

    Just wanted to point out that there is NO need for a temporary variable to swap integers...

    Code:
    void Swap( int &a, int &b)
    {
      a = a ^ b;
      b = b ^ a;
      a = a ^ b;
    }
    Even if you dont want to use this technique, there is still no reason to PASS the temporary...

    Code:
    void Swap( int &a, int &b)
    {
      int tmp = a;
      a = b;
      b = tmp;
    }
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  4. #4
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    Re: Build this simple progam according to earlier standards

    Code:
    int ChangeInteger2(int, int, int); // protocol
    
    {
    int IntegerA;
    int IntegerB;
    int IntegerTemp;
    
    cout << "The value of IntegerB is " << ChangeInteger2(IntegerA, IntegerB, IntegerTemp) << endl;
    
    int ChangeInteger2 (int Integer_A, int Integer_B, int Integer_Temp) // definition
    
    int result2 = Integer_A;
    return result2;
    }
    If you need to define function ChangeInteger2(); then define it as u have defined ChangeInteger();

    "int ChangeInteger2(int, int, int); // protocol" is your declaration. Declaring a function before any function just says u will use the declared function before its defination.

    And search a better logic to "swap two variables".
    Last edited by Mavens; July 22nd, 2007 at 11:35 AM. Reason: Code tags missed

  5. #5
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    Re: Build this simple progam according to earlier standards

    Just wanted to point out that there is NO need for a temporary variable to swap integers...
    Note however that this pertains to integers. The use of a temporary is more typical and generic.

    Even if you dont want to use this technique, there is still no reason to PASS the temporary...
    Tsk tsk, people give out Harry Potter spoilers but you give out swap code spoilers
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  6. #6
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    Re: Build this simple progam according to earlier standards

    Quote Originally Posted by Mavens
    Code:
    int ChangeInteger2(int, int, int); // protocol
    
    {
    int IntegerA;
    int IntegerB;
    int IntegerTemp;
    
    cout << "The value of IntegerB is " << ChangeInteger2(IntegerA, IntegerB, IntegerTemp) << endl;
    
    int ChangeInteger2 (int Integer_A, int Integer_B, int Integer_Temp) // definition
    
    int result2 = Integer_A;
    return result2;
    }
    If you need to define function ChangeInteger2(); then define it as u have defined ChangeInteger();

    "int ChangeInteger2(int, int, int); // protocol" is your declaration. Declaring a function before any function just says u will use the declared function before its defination.

    And search a better logic to "swap two variables".
    What do you mean exactly, it looks to me as if I defined them identically allready.

    Also, could somebody explain to me how this works:

    Code:
    int tmp = a;
      a = b;
      b = tmp;
    Thanks!
    Last edited by Break2; July 22nd, 2007 at 12:47 PM.

  7. #7
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    Re: Build this simple progam according to earlier standards

    You havnt defined that identically.

    A function defination contains
    return type function_name(parameters)
    {
    Internal defination
    return value
    }

    what you have done is
    function_name(parameters); // See a semicolon there
    {
    some Internal defination. // useless stuff.
    started a function defination again. // It seems that u dont know how to define and use a function.
    }

    Explanation of

    int tmp = a; // You have taken a temporary variable in which u put value
    of a.
    a = b; // Now put value of b in a.
    b = tmp; // and finally put value of tmp in a.

    So you hav got value of a and b in b and a respectively. which is called swapping of two variables.

  8. #8
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    Re: Build this simple progam according to earlier standards

    Quote Originally Posted by Mavens
    It seems that u dont know how to define and use a function
    I think you hit the nail right on the spot there. Sometimes I do not know exactly what I am doing when it comes to defining and using a function.

    Some of the absolute noob questions I have are:

    - Do I always need to use a prototype before the 'main' section?
    - I like to keep the prototype and definition seperated, prototype above the main section, definition below main, is this always applicable and good practice?
    - When do I have to use "return 0" and when do I return an actual value?
    - Isn't the left part of the function actually a variable?
    If I for instance have:
    Code:
    char x = (Character_1 + 1)
    Isnt it so that "char x = (Character_1 + 1)" is a function while "char x" is also a variable?

    Yes, yes, I know, absolute noob questions.
    Last edited by Break2; July 23rd, 2007 at 04:28 AM.

  9. #9
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    Re: Build this simple progam according to earlier standards

    Quote Originally Posted by Break2
    - Do I always need to use a prototype before the 'main' section?
    Not always, however, it is a good habit to always use prototypes.

    - I like to keep the prototype and definition seperated, prototype above the main section, definition below main, is this always applicable and good practice?
    Yes. especially once you start creating your own header files.

    - When do I have to use "return 0" and when do I return an actual value?
    That depends entirely on the code you're writing. there's nothing especially meaningful about zero, its just a number. But depending on the context of the function, it can be very useful.

    More useful, possibly, in 'C' style code. Much of the C standard library uses functions which 'return 0;' for various reasons - probably because C didn't have a built in 'bool' type. in C++ i find it less useful, since most situations simply require a true/false value.

    return 0 sometimes works well in conjunction with pointers, although if you're just getting to grips with functions you shouldn't be worrying about pointers for a while yet

    - Isn't the left part of the function actually a variable?
    If I for instance have:
    Code:
    char x = (Character_1 + 1)
    Isnt it so that "char x = (Character_1 + 1)" is a function while "char x" is also a variable?
    No, this is a statement containing an expression. 'x' is a char variable - which is assigned the result of the expression Character_1 + 1

    a function is a named block of code. If you wanted to write a function to perform the above expression, it could look something like this
    Code:
    char my_function(char);    //Function Prototype
    
    int main()
    {
        char my_character = 'C';
        char x = my_function( my_character );  //Statement with a function call
    }
    
    
    //Here is the function itself
    char my_function(char Character_1)
    {
        return Character_1 + 1;
    }
    Yes, yes, I know, absolute noob questions.
    Nothing wrong with asking questions, we were all beginners once I do suggest you read a good tutorial or book which thoroughly explains functions though.
    Last edited by Bench_; July 23rd, 2007 at 08:48 AM.

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