C# E1 CSC 298 Arrays in C#

C# E2 1D arrays  A collection of objects of the same type  array of integers of size 10 int[] a = new int[10];  The size can be specified at run time. int n = ReadInt(); int[] a = new int[n];  An array is a reference type. It is defined on the heap  As in C++ and Java, the first element has index 0.  To iterate through an array (use the Length property) for(int i=0; i<a.Length; i++) { /* work with a[i] */ }

C# E3 Rectangular arrays  Arrays with 2 or more dimensions  array of strings of size 10 by 20 (10 rows by 20 columns) string[,] a = new string[10,20];  Useful properties and methods Length : total number of elements Rank : total number of dimensions GetLength(int dimension) : number of elements in the specified dimension  To iterate through a rectangular array for(int i=0; i<a.GetLength(0); i++) for(int j=0; j<a.GetLength(1); j++) { /*Work with a[i,j]*/ }

C# E4 Jagged arrays  In a 2D rectangular array all rows have the same number of columns.  If this is not desirable, use a jagged array // an array to store the daily rainfall // during March, April and May double[][] a = new double[3][]; a[0] = new double[31]; // March a[1] = new double[30]; // April a[2] = new double[31]; // May // To iterate for(int i=0; i<a.Length; i++) for(int j=0; j<a[i].Length; j++) { /* Work with a[i][j] */ }  Think of a as an array of arrays.

C# E5 Array initialization  The array initializer must be on the line of declaration int[] a = new int[]{1,2,3}; //shorthand int[] a = {1,2,3}; //rectangular 3x2 array int[,] b = new int[3,2]{{1,2},{3,4},{5,6}}; //shorthand int[,] b = {{1,2},{3,4},{5,6}}; // jagged array int[][] c = new int[2][]{new int[]{1,2,3},new int[]{4,5}}; //shorthand (must use new for the inner //arrays) int[][] c = {new int[]{1,2,3},new int[]{4,5}};

C# E6 foreach loop (1)  A convenient construct to iterate through an array string[] a = new string[10]; /* code to initialize a */... // Iterate through a foreach(string s in a) { /* work with s */ }  How would you iterate through a rectangular or a jagged array with this construct?

C# E7 foreach loop (2)  Rectangular array (same as for 1D array) string[,] a = new string[10,20]; /* code to initialize a */... // Iterate through a foreach(string s in a) { /* work with s */ }  Jagged array string[][] a = new string[2][]; a[0] = new string[5]; a[1] = new string[3]; /* code to initialize a */... // Iterate through a (=array of arrays) foreach(string[] arr in a) foreach(string s in arr) { /* work with s */ }

C# E8 Array class  A class that contains many useful methods to work on arrays  A sampling (see the documentation for more details) // Reverse the order of the elements // of a 1D array a Array.Reverse(a); // Find an object o in a 1D array a // o could be an int, a string... // Note: the array must be sorted int index = Array.BinarySearch(a,o); // Sort a 1D array // Note: the elements of the array // must be comparable. Array.Sort(a);

C# E9 ArrayList class (1)  To get an array whose size can change dynamically, use an ArrayList (in System.Collections)  An ArrayList is a dynamic array of objects.  object is the ultimate base class of all objects in C# (more on this soon). All struct and class instances are of type object.  Thus, you can put anything you want in an ArrayList.

C# E10 ArrayList class (2)  Simple example ArrayList a = new ArrayList(); a.Add(4); // a is {4} a.Add("Hello"); // a is {4,"Hello"} Console.Write(a.Count); // 2 is printed a.Remove(a[0]); // a is {"Hello"} a.Add(Color.Red); //a is {"Hello",Color.Red} string s = (string)a[0]; // s is "Hello" a.Remove(Color.Red); // a is {"Hello"} // could also do a.Remove(a[1]);  See the class web site for a more complete example

C# E11 Iterating through an ArrayList ArrayList a = new ArrayList(); // Initialize a... // To iterate, can use a for loop for(int i=0; i<a.Count; i++){ /* work with a[i] */ } // or a foreach loop foreach(object o in a){ /* work with o */ } // Can also use an IEnumerator IEnumerator ietr = a.GetEnumerator(); while(ietr.MoveNext()) { object o = ietr.Current; /* work with o */ }