Arrays and Other Data Structures

1. Arrays and Other Data Structures • Introduction to Arrays • Bounds and Subscripts • Integer Arrays • Floating Point Number Arrays • Lists (Linked) • Stacks

2. Introduction to Arrays • An array is a contiguous block of the same data type. For example, you could have an array of integers (a block of integers), but not a block of integers and floats. • An integer array • int agesOfKids[n]; • Where n is the size of the block indicating the number of integers in this array

3. Bounds and Subscripts • Array Bounds • "Array bounds" refer to the boundaries in memory which the array occupies. The beginning of the array (the first) element is considered the lower bound, while the end (or top) is considered to be the upper bound. • Element • An "element" is an individual entity inside the array. Because C arrays have a lower bound of 0, array[0] refers to the first element. • Array Subscript • The expression inside the [ ... ] is known as an array subscript.

4. EXAMPLE -- To keep monthly high temperatures for all 50 states in one array. int stateHighs [ 50 ] [12 ] ; [ 0 ] [ 1 ] [ 2 ] . . stateHighs [2] [7] . [ 48 ] [ 49 ] [0] [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] 66 64 72 78 85 90 99 105 98 90 88 80 row 2, col 7 might be Arizona’s high for August

5. rows columns STORAGE 8000 8024 8048 12 highs for state 0 12 highs for state 1 etc. Alabama Alaska first row second row const int NUM_STATES = 50 ;const int NUM_MONTHS = 12 ;int stateHighs [ NUM_STATES ] [ NUM_MONTHS ] ; • In memory, arrays are stored in row order. The first row is followed by the second row, etc. Base Address . . .

6. Integer Arrays • We wish to store the 4-digit pager numbers for all 50 apartments in an apartment complex • int[] pager_numbers = new int[51]; • Location zero is reserved for the building manager • pager_number[0] = 2435;

7. Integer Arrays • Suppose that we wish to print all pager numbers from apartment#1 to apartment#50 in a nicely formatted list • The best way to do this would be to use the for loop

8. The for Statement • “for” is a loop statement that is controlled through a loop control variable • for (lcv=1; lcv<=100; lcv++) • The above loop will start with lcv=1 and it will run until lcv equals 100. The step size is 1 (lcv++)

9. Pager Numbers Printout in Java • int[] pagers = new int[50]; • int loop; • for (loop=1; loop<=50; loop++) • System.out.println(pagers[loop]);

10. Lists • Introduction to Lists • Contiguous Lists • Adding and Deleting in Contiguous Lists • Linked Lists • Pointers in Linked Lists • Inserting into a Linked List • Deleting from a Linked List

11. Introduction to Lists • An organization’s membership list may grow and shrink in size. • Your phone book may also grow and shrink in size as time passes • We need a mechanism to store dynamic lists in the memory

12. Linked Lists • Linked lists have entries connected with pointers • Deleting an entry can be implemented by re-arranging pointers • So we leave the entries where they are and just re-align the pointers

13. Pointers • Think about the pointers in your life My mailing address My Home

14. Pointers

15. Pointers • Web links are also pointers UCLA Server Computer http://www.ucla.edu

16. Inserting into a Linked List Header NEXT Bob 242-7111 NEXT Fred 423-3158 New Entry

17. Inserting into a Linked List Header NEXT Bob 242-7111 NEXT Fred 423-3158 New Entry

18. Inserting into a Linked List NEXT NEXT Bob 242-7111 Fred 423-3158 Header

19. Deleting from a Linked List NEXT NEXT NEXT Alice 242-7111 Bob 423-3178 Fred 423-3158 Header

20. Deleting from a Linked List NEXT Bob 423-3178 NEXT NEXT Alice 242-7111 Fred 423-3158 Header

21. Stacks • Stacks • Stack Base and Stack Pointer • Push operation • Pop operation

22. Stacks • A stack is a useful data structure that stores values that may be needed in the near future • For example, you may want to return back to a website that you browsed a few moments ago • You may want to undo an operation that you performed in MS-Word • In a stack, we have a fixed size block of memory available in which we can only add and delete at one end • We keep track of both ends of stack with pointers

23. Stack Operation Other Memory Designated Block for Stack

24. Stack Operation EMPTY STACK SP SB

25. Stack Operation STACK WITH ONE DATA ITEM SP SB Val1

26. Push Operation • We store a data item at the location referenced by SP SP SB Val1

27. Push Operation • We store a data item at the location referenced by SP and then increment SP SP Val2 SB Val1

28. Push Operation • Stack[SP] = New Value • SP= SP+1; • The stack has a fixed maximum size of N locations. We cannot bump into other memory • Therefore, we must check before pushing if the stack is full • How?

29. Push Operation • if (SP == SB+N) • cout “sorry!! Stack is full”; • else • { • Stack[SP] = New_Value • SP= SP+1; • }

30. Pop Operation • We retrieve a data item from the top of stack. How can we reach top of stack value? SP Val3 Val2 SB Val1

31. Pop Operation • Val3 is top of stack and it is one below the current location referenced by SP SP Val3 Val2 SB Val1

32. Pop Operation • Val3 is popped out and SP is decremented to point to newly vacated location SP Val2 SB Val1

33. Pop Operation • Popped_Value = Stack[SP-1]; • SP= SP-1; • We cannot pop from an empty stack so we must check before popping • How?

34. Pop Operation • if (SP == SB) • cout “sorry!! Stack is empty”; • else • { • Popped_Value = Stack[SP-1]; • SP= SP-1; • }

35. Stack Applications • Stacks are very useful in remembering values • Stacks operate similar to the way the office clerks process letters and folders • The current document is on top of stack and it has to be processed first • Stacks help programs remember the place where call to a procedure was issued