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Arrays in C++

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• Defining arrays in C++
  • The syntax to define an one-dimensional array in C++ is:

    TYPE arrayName[ constantSize ];

    Example:

    int a[100]; // array of 100 integers double b[10]; // array of 10 doubles

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    Compare the difference with Java:

    int[] a = new int[100]; // array of 100 integers double[] b = new double[10]; // array of 10 doubles

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• Internal representation of arrays in C++
  • The internal storage of arrays in C++ is also different from Java

  • An array in C++ is stored directly:

    int a[10]; Storage structure in C++:

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  • When an array is defined, the C++ compiler will allocate space to store the array and then record the following information in the array:

    The name of the array (a) The type of the array (int) The address of the first element of the array (2404 in the example)

    Furthermore:

    The address of the first element of the array cannot be changed (This address is recorded by the C++ compiler and it is fixed after the array is defined) In other words: arrays in C++ are static (location is fixed after its creation)

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  • Compare the difference with Java:

    An array in Java is stored indirectly:

    int[] a; // defines variable a a = new int [10]; // record location of array in a Storage structure in Java:

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• Accessing array elements in C++
  • The syntax to access individual array elements in C++ is the same as Java

    Example:

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    Example: Find smallest element in an array

    int a[10]; int min, i; min = a[0]; for ( i = 0; i < 10; i++ ) { if ( a[i] < min ) min = a[i]; } cout << "min = " << min << endl;

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  • Example Program: (Demo above code)                                                
    • Prog file: click here

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• Extremely important notice
  • Important difference in array between C++ and Java:

    C++ does not perform run time array bound checks (While Java does perform run time array bound checks)

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  • C++ is designed for speed

    When you access an array element a[i], the index i may be out of bound

    Java inserts code in the program to perform runtime array bound checks and an out of bound array index will cause a run time error

    run time array bound checks will slow down a program !!!

    C++ does not perform runtime array bound checks !!!

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  • Example Program: (Demo above code)                                                
    • a C++ Prog file with index out of bound error: click here
    • a Java Prog file with index out of bound error: click here

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  • Again, you must be more responsible when programming with C++