Help with a decimal to binary converter

This is a discussion on Help with a decimal to binary converter within the C++ Programming forums, part of the General Programming Boards category; Hi all, I would really appreciate help with the following code, Im very new to programming (2nd week actually!) and ...

  1. #1
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    Help with a decimal to binary converter

    Hi all,

    I would really appreciate help with the following code, Im very new to programming (2nd week actually!) and I cant seem to resolve a problem I am currently having! I would like to convert a decimal number to binary, but the output is (obviously) not correct for decimals that are not completely factorized for 2^x. For instance the decimal '4' will return the correct answer of "1-0-0" yet '6' will return the same number!? Ive poured over my code numerous times and there seems to be nothing wrong with my logic...
    Thanks a million to anyone that wouldnt mind helping a complete newbie!

    Code:
    // Daniel Erasmus
    // 0703393 W
    // Decimal --> Converter
    // 21/02/08 08:24
    
    # include <iostream>
    # include <math.h>
    
    using namespace std;
    
    int main ()
    {
        int decimal;
        int x;
    
        cout << "Welcome to the Decimal ----> Binary converter!" << endl << endl;
    
        cout << "Please enter decimal to be converted: ";
        cin >> decimal;
        cout << endl << endl;
    
        x = log (decimal+1) / log (2);
    
        for ( int y = pow (2, x) ; x >= 0 ; x--)
        {
            int m = decimal / y;
    
            if ( m >= 1 )
            {
                decimal = (decimal - y);
                cout << "1";
            }
            else if (m < 1 )
            {
                cout << "0";
            }
        }
    cin.get ();
    }
    On an unrelated note: I wonder if anyone could explain how to open a program from c++, ie: I have created a password pretection program and to try it out I would like a word document (in MS word) to open when the correct password is entered!!

    Thanks again!!!!
    Last edited by danielerasmus; 02-23-2008 at 02:08 AM. Reason: mistake

  2. #2
    Deathray Engineer MacGyver's Avatar
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    You're messing something up with your implicit conversions from double to int I believe, although your method of using log() only to use pow() seems somewhat convoluted.

    Quote Originally Posted by danielerasmus View Post
    On an unrelated note: I wonder if anyone could explain how to open a program from c++, ie: I have created a password pretection program and to try it out I would like a word document (in MS word) to open when the correct password is entered!!
    There are a number of ways. One is using system(). It's the most portable, but probably the least recommended. For Windows specifically, there are functions like ShellExecute() and ShellExecuteEx(). I believe the "most proper way" to actually start a process yourself in Windows is using CreateProcess().

  3. #3
    CSharpener vart's Avatar
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    and of course to convert integer to binary using float fuctions like pow instead of simple bit-operations is a lot of overkill
    The first 90% of a project takes 90% of the time,
    the last 10% takes the other 90% of the time.

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    thanks guys, but the debugger says the variables are at the correct values!! Im really not sure whats going wrong - and any and all help would be greatly appreciated!

  5. #5
    Deathray Engineer MacGyver's Avatar
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    You're not updating y every iteration.

  6. #6
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    If you're working with bits you should use the bit operators. It's easier and faster.
    Code:
    #include <iostream>
    
    using namespace std;
    
    // Return a value with the bit specified
    // by i set and all other bits unset
    inline unsigned int bitmask ( int i )
    {
        return (1U << i);
    }
    
    int main()
    {
        // The number of bits in an int
        const int intSize = 31;
    
        // The decimal number to convert
        int value;
    
        cout << "Please enter a decimal number to be converted: ";
        cin >> value;
    
        // Print the bits of the decimal value
        for ( int i = intSize; i >= 0; --i )
        {
            // Assume bitmask( i ) is unset
            char bit = '0';
    
            // Pick the character to print
            if ( value & bitmask( i ) )
            {
                bit = '1';
            }
    
            cout << bit;
        }
    
        cout << endl;
    
        return 0;
    }

  7. #7
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    thanks macgyver, i put the y updating expression inside the actual loop - thanks so so much! Im just not a hundread percent sure why it wasnt working before surely after each iteration of the loop the decleration of the variable is overwritten and updated??? :- )

  8. #8
    Deathray Engineer MacGyver's Avatar
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    Review for loops. The initialization part of the loop is only done once at the start right before the first iteration.

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