Thread: problem on dynamic array

  1. #1
    Registered User
    Join Date
    Oct 2006

    problem on dynamic array

    This is the code I saw in mock paper.
    struct Ant
         int age, strength;
    int n;
    cin >> n;
    Ant *AntArmy;
    AntArmy = new Ant[n];//can't get why the structure name can be the array name
    What is the difference between class & struct?
    Why is the structure name used as the array name?
    What 's going on with AntArmy = new Ant[n];?
    Thanks in advance!

  2. #2
    Registered User
    Join Date
    Jun 2005
    The difference between class and struct is that everything in a class is private by default, but everything in a struct is public by default. Other than that a C++ class and a C++ struct are identical.

    The structure name is not used as an array name. The line "AntArmy = new Ant[n];" is an instruction to dynamically allocate and construct and array of n Ant's, and then give AntArmy a value which is the address of the first element in that dynamically allocated array.

  3. #3
    (?<!re)tired Mario F.'s Avatar
    Join Date
    May 2006
    To add to what grumpy said, pay attention to these two lines

    Ant *AntArmy;
    AntArmy = new Ant[n];
    AntArmy is first declared to be a pointer to the Ant type.
    Then AntArmy is assigned the the first element of a dynamically allocated array of Ant types.

    The expression new Ant[n] allocates an array of Ant types and returns a pointer to the first element

    AntArmy is assigned that pointer.

    That would have been the same as simply writing:

    Ant* AntArmy = new Ant[n];
    Originally Posted by brewbuck:
    Reimplementing a large system in another language to get a 25% performance boost is nonsense. It would be cheaper to just get a computer which is 25% faster.

  4. #4
    Registered User
    Join Date
    Oct 2006
    Thank you for your clear explanation, I got it.

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