Arrays

This chapter introduces arrays, a common multi-dimensional data structure used to store data of the same type. (Note that a class is a "data type" in this sense.) Arrays have some number of dimensions and a number of elements in each dimension. These are established when the array is created. The range of the array's index in each dimension goes from zero to the number of that dimension's elements minus one. A for loop is commonly used to initialize, manipulate, and access the values in an array. Here, we treat one-dimensional arrays, sometimes called vectors.

2. Picture of an Array



Answer:
Probably not. It would be useful to have an organized way of reading and storing the values.






Picture of an Array



    

        

        

        

            

        

    





    
array0An array is an object that is used to store a list
        of values.

    
An array is made out of a contiguous block of memory that is divided into a number of cells. Each cell holds a value, and all the values are of the same type. Sometimes the cells of an array are called slots. In the
        example array pictured at right, each cell holds an int.

    
The reference variable that points to this array is named data. Sometimes the identifier "data" is called "the name of the array" although it is really the name of a reference variable.

    
The cells are indexed 0 through 9. Each cell can be accessed by using its index. For example, data[0] is the cell which is indexed by zero (which contains the value 23). data[5] is the cell
        which is indexed by 5 (which contains the value 14).

    
Facts:

    
    
        
      
            
        
                
      • The cells are numbered sequentially starting at zero.
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      • If there are N cells in an array, the indexes will be 0 through N-1.
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      • The length of an array is the number of cells.
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Sometimes the index is called a subscript. The expression data[5] is usually pronounced "data-sub-five" as if it were an expression from mathematics: data5.

    
The value stored in a cell of an array is sometimes called an element of the array. An array has a fixed number of cells. The values in the cells (the elements) can be changed.

    
An array is a full-blown object, and consists of more than just its cells. For example, the length instance variable holds the number of cells of the array. For the above array, data.length holds the
        value 10.





Question 2:
What value is in data[7] ?