CIS162AD - C#

1. CIS162AD - C# Arrays – part 112_arrays_loading.ppt

2. Overview of Topics • Declaring Arrays • Loading Arrays • Partially Filled Arrays • Arrays Elements as Arguments • Declaring and Loading Constant Arrays

3. Arrays are Tables • Array is a different word for a table. • A table is made up of columns and rows. • Just like an Excel spreadsheet.

4. 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.

5. Declaring Array int intQty1, intQty2, intQty3;int[ ] intQty = new int[3]; //3 integer variablesdataType[ ] 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.

6. Array Subscript dataType[ ] arrayName = new dataType[arraySize]; • Arrays are allocated consecutive memory. • Each element is referenced using a subscript. • Subscript are integers. • The number of elements that are created is arraySize. • The first element in the array is referenced with a value of zero [0]. • The last element is referenced with a subscript value of [arraySize – 1]. • A subscript is also referred to as an index. • Short variable names for subscripts are acceptable.

7. Memory Map

8. 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.

9. Preventing Out of Range • C# will not prevent a subscript out of range error, but it will abort the execution when it happens. • It aborts because the subscript would be referencing some other section of memory than what was allocated for the array. • The programmer is responsible for preventing the out range error. • We can use some built in methods to manage arrays, arrayName.Length arrayName.GetUpperBound(0). • The For Each (foreach) command may also be used to walk through arrays.

10. Array Properties 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)

11. Array Processing • Declare Array • 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. • 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.

12. Declare Array //Arrays are declared at the class level, //so they can be referenced by all methods.int[ ] cintTestScores = new int[20];int cintNumberOfStudents; //We can load up to 20 scores, but we will //save how many tests are actually loaded in cintNumberOfStudents.

13. Declare Array with a Const //Arrays can be declared using a constant for the size.const int intARRAY_SIZE = 20;int[ ] cintTestScores = new int[intArraySize];//We can still load up to 20 scores

14. cintTestScores Array Memory Map

15. Load Array cs12ex.txt 5040100301020 //Loads Array with scores saved in a data file. private void btnLoadArray_Click( ) {FileStream studentFile = new FileStream("cs12ex.txt", FileMode.Open); StreamReader studentStreamReader = new StreamReader(studentFile); int i = 0; //subscript initialized to zerowhile (studentStreamReader.Peek() != -1){ if (i < cintTestScores.Length) {cintTestScores[i] = int.Parse(studentStreamReader.ReadLine( )); i ++; //Increment subscript by one } else { MessageBox.Show (“Array Size Exceeded”); break; //Get of out of loop; Array is full. }}cintNumberOfStudents = i; //Save how many students were loadedstudentFile.Close( ); //Close file }

16. Loaded Arrays

17. 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”); }

18. For Each - Example private void btnProcessArray_Click( ) {int i; //subscript not neededint intSum = 0; foreach (int intTestScore in cintTestScores){ intSum += intTestScore; } txtSum.Text = intSum.ToString(“N0”); }

19. 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); }

20. 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.

21. Load Array – Partially Filled //Loads Array with scores saved in a data file. private void btnLoadArray_Click( ) {FileStream studentFile = new FileStream("cs12ex.txt", FileMode.Open); StreamReader studentStreamReader = new StreamReader(studentFile); int i = 0; //subscript initialized to zerowhile (studentStreamReader.Peek() != -1){ if (i < cintTestScores.Length) {cintTestScores[i] = int.Parse(studentStreamReader.ReadLine( )); i ++; //Increment subscript by one } else { MessageBox.Show (“Array Size Exceeded”); break; //Get of out of loop; Array is full. }}cintNumberOfStudents = i; //Save how many students were loadedstudentFile.Close( ); //Close file }

22. Processing Partially Filled Arrays private void btnProcessArray_Click( ) {int i;int intSum; //for (i = 0; i <= cintTestScores.GetUpperBound(0); i++) //process entire arrayfor (i = 0; i <mintNumberOfStudents; i++) //process partially filled array{ intSum += cintTestScores[i]; } txtAverage.Text = (intSum / mintNumberOfStudents).ToString(“N0”); }

23. Declare and Load Constant Arrays • Arrays that will hold constants or some initial values can be loaded at declaration. • When the values are provided at declaration, do not include the size. The size is determined by the number of values provided. • The values are enclosed in braces and not parenthesis.decimal[ ] cdecPERCENT_RANGE = new decimal[ ] {90D, 80D, 70D, 60D, 0D};string[ ] cstrLETTER_GRADE = new string[ ] {"A", "B", "C", "D", "F"}; • C# does NOT allow const for arrays.

24. Summary • Declaring Arrays • Loading Arrays • Partially Filled Arrays • Arrays Elements as Arguments • Declaring and Loading Constant Arrays