Understanding Output Generated

This is a discussion on Understanding Output Generated within the C Programming forums, part of the General Programming Boards category; Hello, I'm slightly confused with the concept of Hexadecimal. It is assumed that the addresses of the variables i, j ...

  1. #1
    Air
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    Understanding Output Generated

    Hello, I'm slightly confused with the concept of Hexadecimal. It is assumed that the addresses of the variables i, j and the first element of the integer array num in hexadecimal are 22FF6C, 22FF68, 22FF40 respectively.

    Code:
    int i, j = 3;
    int *pi = &i, *pj = &j;
    int num[5]={25, -1, 3, 12, 100};
    printf("%x, %x, %x\n", &i, &j, num);
    printf("%x, %x\n", pi, pj);
    j++;
    *pj *= 3;
    printf("%x, %d\n", pj, *pj);
    pi = num;
    num[0] += 5;
    printf("%x, %d\n", pi, *pi);
    printf("%x, %d\n", pi+j, *pi+j);
    How does the output change from 22FF40 to 22FF70? I don't understand that part. Could someone explain. Thanks in advance, Air.

  2. #2
    CSharpener vart's Avatar
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    And where is your output? You do not suppose any compiler on any OS will produce same output with the code above?
    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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    Air
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    I know, but the data is given.

    It is assumed that the addresses of the variables i, j and the first element of the integer array num in hexadecimal are 22FF6C, 22FF68, 22FF40 respectively.
    I would be greatful if anyone could explain the change from 22FF40 to 22FF70.

  4. #4
    and the Hat of Guessing tabstop's Avatar
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    You mean there where you do pi+j at the bottom? You're adding to a value and you don't understand why it's bigger? Specifically, j is 12 at this point in the program, and 12 addresses past 22FF40 is 22FF70.

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    CSharpener vart's Avatar
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    Quote Originally Posted by Air View Post
    I know, but the data is given.



    I would be greatful if anyone could explain the change from 22FF40 to 22FF70.
    You forgot to tell where this change occured. I do not see the 22ff70 anywhere...
    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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    Air
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    Quote Originally Posted by tabstop View Post
    You mean there where you do pi+j at the bottom? You're adding to a value and you don't understand why it's bigger? Specifically, j is 12 at this point in the program, and 12 addresses past 22FF40 is 22FF70.
    Yes, I understand that j is 12 at this point. But when you mean 12 address, how is it added?

    22FF40 + 12 = 22FF(40+12) = 22FF52?

  7. #7
    and the Hat of Guessing tabstop's Avatar
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    pi points to an int, ints take up four bytes of room. So after 22FF40, the next (int) address is 22FF44, then 22FF48, then 22FF4C, etc.

    (If it was chars, then you would only add 12, since chars take up only one byte. Of course 22FF40 plus twelve is 22FF4C, not 22FF52.)

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    Air
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    Quote Originally Posted by tabstop View Post
    pi points to an int, ints take up four bytes of room. So after 22FF40, the next (int) address is 22FF44, then 22FF48, then 22FF4C, etc.

    (If it was chars, then you would only add 12, since chars take up only one byte. Of course 22FF40 plus twelve is 22FF4C, not 22FF52.)

    Which letter is last? From 22FF48, it goes to 49, 4A, 4B, 4C. Which is the last letter?

  9. #9
    CSharpener vart's Avatar
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    Quote Originally Posted by Air View Post
    Which letter is last? From 22FF48, it goes to 49, 4A, 4B, 4C. Which is the last letter?
    It is not a letter - it is hexamal digit

    A = 10
    B = 11
    C = 12
    D = 13
    E = 14
    F = 15
    The first 90% of a project takes 90% of the time,
    the last 10% takes the other 90% of the time.

  10. #10
    Air
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    Quote Originally Posted by vart View Post
    It is not a letter - it is hexamal digit

    A = 10
    B = 11
    C = 12
    D = 13
    E = 14
    F = 15

    Aah, I see. 15 is the last? Then I assume it goes to: 22FF50, 22FF51, 22FF52, 22FF53, 22FF54, 22FF55, 22FF56, 22FF57, 22FF58, 22FF59, 22FF5A, 22FF5B, 22FF5C, 22FF5D, 22FF5E, 22FF5F, 22FF60

  11. #11
    Air
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    Just did it manually. Worked out F=15 is last. Thank you both for taking time out to help me. You have both been very clear and patient. Thanks once again.

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