map objects


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Thread: map objects

  1. #1
    clay Guest

    map objects


    could you explain the operation of the following function:

    typedef map<int, double> maptype;
    typedef pair<const int, double> Pair;

    int main()
    {
    Pair a[3] =
    { Pair(20, 1.5),
    Pair(800, 0.3),
    Pair(3, 0.2)
    };
    maptype MA;
    maptype MB(a, a + 3);
    maptype MC(MB);
    cout << MC[800] << endl;
    return 0;
    }


  2. #2
    Igor Soukhov Guest

    Re: map objects


    Hi clay !
    "clay" <magilla@cfl.rr.com> wrote:
    >could you explain the operation of the following function:

    Sure ! =)

    >typedef map<int, double> maptype;
    >typedef pair<const int, double> Pair;


    >
    >int main()
    >{
    > Pair a[3] =
    > { Pair(20, 1.5),
    > Pair(800, 0.3),
    > Pair(3, 0.2)
    > };
    > maptype MA;
    > maptype MB(a, a + 3);

    initialize map with array's data
    these code can be replaced with this code:

    maptype MB;
    MB[20] = 1.5;
    MB[800] = 0.3;
    MB[3] = 0.2;

    > maptype MC(MB);

    create a copy of MB

    > cout << MC[800] << endl;

    "0.3" should be printed

    > return 0;
    >}



  3. #3
    Danny Kalev Guest

    Re: map objects



    clay wrote:
    >
    > could you explain the operation of the following function:


    a map is an associative array that binds two values: a key and its
    associated value. These two values are called pairs. in your example,
    the map contains pairs of int and double. In other words, the int is a
    key and the double is the value associated with it.
    >
    > typedef map<int, double> maptype;
    > typedef pair<const int, double> Pair;
    >
    > int main()
    > {
    > Pair a[3] =
    > { Pair(20, 1.5),
    > Pair(800, 0.3),
    > Pair(3, 0.2)
    > };
    > maptype MA;
    > maptype MB(a, a + 3);

    in the above line the map is populated with three pairs -- the elements
    of the array a.

    > maptype MC(MB);

    MB is copied into a new map called MC.

    > cout << MC[800] << endl;


    The pair a[1] has the key 800 and the associated value 0.3. This line
    prints the value associated with the key 800, namely 0.3.

    Danny

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