Arrays: Declaring, Loading, and Processing in C#, Slides of C programming

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Arrays – part 1

12_arrays_loading.ppt

Overview of Topics

• Declaring Arrays
• Loading Arrays
• Partially Filled Arrays
• Arrays Elements as Arguments
• Declaring and Loading Constant Arrays

Array Defined

• An array is used to process a collection

of data all of which is of the same data

type (Integer, Decimal, String, etc.).

• First we’ll look at single dimensional

arrays (one column, many rows).

• Think of a single dimensional array as a

list of variables.

Declaring Array

int intQty1, intQty2, intQty3;

int[ ] intQty = new int[3]; //3 integer variables

dataType[ ] arrayName = new dataType[arraySize];

• An array of 3 elements of type integer is created.
• The arraySize is used by C# to determine how much

memory to allocate.

• Arrays will usually be class-level because after values

are loaded in we don’t want to lose the values.

Memory Map

• 1010 intQty1 Address Variable Value
• 1020 intQty2
• 1030 intQty3
• 1040 intQty[0]
• 1050 intQty[1]
• 1060 intQty[2]
• 1070 decPrice

Subscript Out Of Range

• If during execution, the subscript value

referenced an element past the end of the

array, the program would throw an

exception (run-time error).

• The programmer must make sure that the

logic in the program does not allow the

subscript to exceed the array size.

• This is called being out of range.

Array Class Properties & Methods

int[ ] intQty = new int[3]; //3 integer variables

• arrayName.Length
  • intQty.Length is equal to 3.
  • intQty.Length is the number of entries that can be loaded.
  • The last valid subscript value is one less than Length.
• arrayName.GetUpperBound(0).
  • intQty.GetUpperBound(0) is equal to 2.
  • intQty.GetUpperBound(0) is last valid subscript value.
• Depending the loop structure, we may use:
  • less than Length or
  • Equal to GetUpperBound(0)

Array Processing

1. Declare Array
2. Load Array
   • After creating the array, data must be loaded.
   • Use arrayName.Length or arrayName.GetUpperBound(0) to prevent out of range errors.
   • Note: Arrays can be declared and loaded with constant values.
3. Process Array
   • Use individual elements in calculations or as arguments.
   • Send entire arrays to methods for processing.
   • Sort, Search, Display
   • Use a lot of For loops or For Each loops.

Declare Array with a Const

// Arrays can be declared using a constant for the size.

const int intARRAY_SIZE = 20;

int[ ] cintTestScores = new int[i ntArraySize ];

//We can still load up to 20 scores

cintTestScores Array Memory Map

Position Address Index Value 1 1010 [0] 0

2 1014 [1] 0

3 1018 [2] 0

4 1022 [3] 0

5 1026 [4] 0 6 1030 [5] 0

7 1034 [6] 0

… … … …

20 1086 [19] 0

Loaded Arrays

Position Address Index Value

1 1010 [0] 50

2 1014 [1] 40

3 1018 [2] 100

4 1022 [3] 30

5 1026 [4] 10

6 1030 [5] 20

7 1034 [6] 0

… … … …

20 1086 [19] 0

Process Array – Individual Elements

private void btnProcessArray_Click( )

{ int i; int intSum = 0;

for (i = 0; i <= cintTestScores.GetUpperBound(0); i++) { intSum += cintTestScores[i]; }

txtSum.Text = intSum.ToString(“N0”);

}

Individual Elements as Arguments

private void btnProcessArray_Click( )

{ int i; decimal decPercent;

for (i = 0; i <= cintTestScores.GetUpperBound(0); i++) { decPercent = calcPercent( cintTestScores[i] ); txtPercent.Text = decPercent.ToString(“N0”); }

}

private decimal calcPercent(int intScore )

{ return (intScore / 100);

} Docsity.com

Partially Filled Arrays

• In the for loop on the prior slide it was assumed that the arrays were filled by going up to GetUpperBound(0).
• Up to 20 scores could be loaded, but in the example only 6 scores were actually loaded.
• When the array is not full, it is considered a partially filled array.
• The for loops need to be modified to only process the number scores loaded.
• The number of scores loaded are counted in the load routine, and the count should then be saved in a variable like cintNumberOfStudents.
• This variable should then be used when processing the arrays.