• Variable:
  • A named space for holding data/information
  • The name is often referred to as the identifier
• Literal:
  • A representation of a datum
• Assignment:
  • Placing a value into the memory identified by a variable/constant

    income1 = 550.75;
    income2 =  25.60;
    income3 = 347.10;
    income4 = 120.45;
    income5 = 885.00;
    income6 =  10.99;
    income7 = 123.45;
    

• An Observation:
  • Situations like the one above, in which we have collections of similar information, are very common
• Naming Such Collections:
  • We'd like to be able to give the items similar names
  • Naming schemes like the one above are "messy" and not very flexible

• Awful:
  • \(t = a + b + c + d + e\)
• Messy:
  • \(t = x\text{1} + x\text{2} + x\text{3} + x\text{4} + x\text{5}\)
• Better:
  • \(t = x_1 + x_2 + x_3 + x_4 + x_5\)
• Why is it Better?
  • It is possible to refer to a generic element as \(x_i\)(where \(i\) is also a variable)
  • It makes it clear that the different variables are related
  • It makes it possible to use short-hand notation like: \(t = \sum_{i=1}^{n} x_i\)

An array is a contiguous block of memory that can be used to hold multiple homogeneous elements.

• Declaration using the [] Modifier:
  • Syntax: base_type[] array_name;
  • Example: int[] income;
• Accessing Elements using the [] Operator:
  • Syntax: array_name[index]
  • Example: income[5] = 250000;
  • Example: total = income[3];
• A Reminder About Indexes:
  • 0-based (i.e., the "first" element has an index of 0)

One can declare an array and assign all of the elements to it using an "array literal" (formally, an array initializer) as follows:

    char[]   course = {'C','S','1','3','9'};
    int[]    age    = {18, 21, 65};
    

One can then assign elements or access elements using the [] operator.

One can declare an array and assign default values to all of the elements to it as follows:

    char[]   course;
    int[]    age;

    course = new char[5];
    age    = new int[3];
    

One can then assign elements or access elements using the [] operator.

    int[] income;

    income = new int[7];

    income[0] = 550.75;
    income[1] =  25.60;
    income[2] = 347.10;
    income[3] = 120.45;
    income[4] = 885.00;
    income[5] =  10.99;
    income[6] = 123.45;
    

• Using the "Messy" Approach:
  • The error will be detected at compile-time because the name won't have been declared
• Using Arrays:
  • The error won't be detected until run-time (i.e., when the index that is out of bounds is used an ArrayIndexOutOfBounds "error" will be generated)