Arrays

1. Arrays Ch 8

2. Array • A group of variables (elements) of the same type • Reference type!

3. Declaring & Creating an Array • Declaring an array reference double[] hours; • Instantiating array object using new hours = new double[5];

4. Initializing an Array • Declaring, instantiating, and initializing double[] hours; hours = new double[5] {10.5, 21.5, 45, 37, 40}; • Simplified syntax double[] hours = {10.5, 21.5, 45, 37, 40};

5. Memory Allocation ?[4] 40 ?[3] 37 ?[2] 45 ?[1] 21.5 ?[0] 10.5 hours

6. Elements of an Array • Indexed starting at 0, not 1! • The Length property tells the number of elements for(int i=0; i<hours.Length; i++) total += hours[i];

7. foreach Loop • Loops through the elements of an array or collection • Simpler than for loop foreach(double h in hours) total += h;

8. Array Example

10. Result

11. Implicitly Typed Variable • Indicated by keyword var, rather than a particular type • The compiler infers the type of the variable. • Example for (var counter=0; counter<array.Length; counter++) • The compiler infers the type of counter is int, because it’s initialized with an int value.

12. Passing Arrays or Array Elements to Methods • Array is a reference type! • Type of array elements may be a value type or reference type • double[] hours; • GradeBook[] gradeBooks;

13. Passing Arguments • Value type, pass-by-value • Caller's variable CANNOT be changed • Value type, pass-by-reference • Caller's variable CAN be changed • Reference type, pass-by-value • Caller's object content CAN be changed • Caller's reference CANNOT • Reference type, pass-by-reference • Both caller's object and reference CAN be changed

14. Example: Passing Arrays or Array Elements

17. Result

18. Passing Arrays by Value and by Reference • Passing by value • Caller's array elements CAN be changed • Caller's array reference CANNOT • Passing by reference • Both caller's array reference and elements CAN be changed

19. Passing Arrays by Value and by Reference

27. Result

28. Multidimensional Arrays • Two-dimensional • Rectangular array • Jagged array • High dimensional arrays are rare

29. Rectangular Array • Has m rows and n columns int[,] a = new int[3, 4];

30. Jagged Array • An array of arrays • A one-dimensional array • Each element refers to a 1D array • Rows of different lengths

31. Jagged Array Example int[][] jagged = {new int[] {1, 2}, new int[] {3}, new int[] {4, 5, 6 } };

32. Rectangular and Jagged Arrays

35. Result

36. Summary • Array • Group of elements of the same type • Passing array or array element to method • By value • By reference • Multidimensional array • Rectangular or Jagged