HELP > How to remove element in a Structure Array

Hi All,

I'm doing a project creating a 'Library of Books'.

How should I go about 'removing' a book from my current library if let's say, a user has 'borrowed' a book?

Many thanks!!

Code:

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struct info{
        char title[99];
        char author[99];
        char publisher[99];
        char subject[5];
        char index[99];
        int page;
        char location[99];
        char type[99];
        float price;

} books[N] = {
        {"Upgrading and Repairing PCs", "Scott K. Muller", "Que Publishing", "COM", "C112.50COM", 1458, "A-C", "For Circulation", 75.50},
        {"Law : Fundamental Rights and Freedoms", "Charlotte R. Coombs", "IPI Publishing", "LAW", "L145.76LAW", 159, "J-L", "For REFERENCE Only!"},
        {"Matrix Methods", "Eugene O. Trytyshnikov", "World Scientific", "MATH", "M211.91MATH", 560, "M-O", "For Circulation", 80.50},
        {"Arts With The Brain In Mind", "Eric L. Jensen", "ASCD", "ARTS", "A871.96ARTS", 140, "A-C", "For Circulation", 25.00},
        {"A Guide to Physics Problems", "Sidney B. Cahn", "Plenum", "PHY", "S109.87PHY", 351, "S-U", "For Circulation", 63.00},
        {"Geography : History & Concepts", "Arild H. Jensen", "SAGE", "GEO", "G314.55GEO", 255, "G-I", "For Circulation", 55.50},
        {"A History of Australia", "Manning S. Clark", "Melbourne University", "HIS", "H539.23HIS", 572, "G-I", "For REFERENCE Only!"},
        {"Gray's Anatomy", "Henry J. Gray", "Harcourt", "MED", "S280.111MED", 474, "S-U", "For Circulation", 105.40},
        {"The Japanese Langugage", "Anthony E. Backhouse", "Oxford University", "ARTS", "A705.51ARTS", 196, "A-C", "For REFERENCE Only!"},
        {"Programming Pearls", "Scott K. Muller", "Que Publishing", "COM", "C257.69COM", 252, "A-C", "For Circulation", 40.00},
        {"Space & Order", "Steen P. Eiler", "MIT Press", "ARC", "B113.36ARC", 202, "A-C", "For Circulation", 62.00},
        {"Mental Disorder", "Frank C. Krout", "Broadway House", "MED", "S311.64MED", 149, "S-U", "For Circulation", 33.70},
        {"Thomas Calculus", "George B.Thomas", "Addison-Wesley", "MATH", "M216.88MATH", 831, "M-O", "For Circulation", 90.90},
        {"Carnivores", "Jonathan G. Kingdom", "University of Chicago", "ZOO", "S256.17ZOO", 311, "S-U", "For Circulation", 58.00},
        {"General Chemistry", "Linus J. Pauling", "Pan American", "CHEM", "S211.19CHEM", 115, "S-U", "For Circulation", 57.00}
};

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Quote:

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Originally Posted by Inneart

Hi All,

I'm doing a project creating a 'Library of Books'.

How should I go about 'removing' a book from my current library if let's say, a user has 'borrowed' a book?

---

Identify the element to be removed.
Write a loop to move the next and all following elements forward one position in the array.
Mark the last position as unused in some manner.

Do you mean 'borrowed' as in they'll never return it, or 'borrowed' as in checked it out? The latter is normal operation for a library, and because the book is technically still owned by the library, removing it from the list is nonsensical. A flag saying that it's checked out or a due back date would both be better options than removal.

If it's the former, what kind of neighborhood is your library in where that's a use case for the tracking software? :p

Perhaps you don't need to remove it at all. You could have a flag in your structure to indicate that a book is in or out of the library instead of moving things around.

The books don't seem to be in any sorted order, so if you really want to remove an element, you could just copy the last valid element into the element being removed. You will need to maintain a variable holding the index of the last valid element.

An array is not the ideal data structure for this operation as you may have already noticed. If you have to use arrays though, I suggest doing what CommonTater suggested, which is define a sentinel value that is invalid within the scope of your program. If you cannot have "holes" within your array (i.e. invalid values) then you have to copy over all the elements following the position you are removing at one position to the left. Note that this is very expensive computationally O(n) where n is the size of your array.

its trivial like

Code:

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void removeAt(struct info *b, int at, int end)
{
  memmove(&b[i],&b[i+1],(end-at-1)*sizeof*b);
  memset(&b[end-1],0,sizeof*b);
}

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where end is in your case "N" and at is 0 based.