Exam practice

Exam 1  Describe how a Boolean expression can control the operation of a loop  Describe the difference between a while loop and for loop  Explain the dangers of using global variables  In terms of function explain what a parameter is  Explain the difference between passing parameters by reference and by value  Explain the difference between a class and an object 159  Describe how a Boolean expression can control the operation of a loop  Describe the difference between a while loop and for loop  Explain the dangers of using global variables  In terms of function explain what a parameter is  Explain the difference between passing parameters by reference and by value  Explain the difference between a class and an object 159

Search algorithms  Linear search: involves methodically searching one location after another until the searched for value is found. It starts at the beginning of a list and checks each item in turn until the desired item is found. E FOUND AT LOCATION 4 WHAT LOCATION IS D DFCAEBHG

PSEUDOCODE  POINTER=0  WHILE POINTER<LENGTHOFLIST AND LIST[POINTER]!=SEARCHEDFOR  ADD ONE TO POINTER  ENDWHILE  IF POINTER>=LENGTHOFLIST THEN  PRINT(“ITEM IS NOT IN THE LIST”)  ELSE  PRINT(“ITEM IS AT LOCATION “+POINTER)  ENDIF  POINTER=0  WHILE POINTER<LENGTHOFLIST AND LIST[POINTER]!=SEARCHEDFOR  ADD ONE TO POINTER  ENDWHILE  IF POINTER>=LENGTHOFLIST THEN  PRINT(“ITEM IS NOT IN THE LIST”)  ELSE  PRINT(“ITEM IS AT LOCATION “+POINTER)  ENDIF

 Binary search works by dividing the list in two each time until being searched for is found. For binary search to work the list has to be in order.

 LOWERBOUND=0  UPPERBOUND=LENGTHOFLIST-1  FOUND=FALSE  WHILE FOUND==FALSE AND LOWERBOUND!=UPPERBOUND  MIDPOINT=ROUND(LOWERBOUND+UPPERBOUND)/2)  IFLIST[MIDPOINT]==SEARCHEDFOR THEN  FOUND=TRUE  LOWERBOUND=0  UPPERBOUND=LENGTHOFLIST-1  FOUND=FALSE  WHILE FOUND==FALSE AND LOWERBOUND!=UPPERBOUND  MIDPOINT=ROUND(LOWERBOUND+UPPERBOUND)/2)  IFLIST[MIDPOINT]==SEARCHEDFOR THEN  FOUND=TRUE

Insertion sort: Divide the list into two parts sorted and unsorted and insert it in the correct position in the sorted section.  Make the first item the sorted list, the remaining items are the unsorted list.  WHILE there are items in the unsorted list  Take the first item of the unsorted list.  WHILE there is an item to the left of it which is smaller than itself  Swap with that item  END WHILE  The sorted list is now one item bigger  END WHILE  Make the first item the sorted list, the remaining items are the unsorted list.  WHILE there are items in the unsorted list  Take the first item of the unsorted list.  WHILE there is an item to the left of it which is smaller than itself  Swap with that item  END WHILE  The sorted list is now one item bigger  END WHILE

CABEFD UNSORTED SORTED ACBEFD UNSORTED SORTED ABCEFD UNSORTED

Merge sort: Splits the size n into n lists of size 1. Each of these lists is merged with another. Each of the newly merged lists is merged with another. This is repeated until there is only one, sorted list. The key to this algorithm is the way the lists are merged.

Merge sort  IF the first item in list1<the first item in list2  THEN  Remove the first item from list1 and add it to newlist  ELSE  Remove the first item from list2 and add it to newlist  ENDIF  ENDWHILE  IF list1 is empty THEN  Add the reminder of LIST2 to newlist  ELSE  ADD the remainder of list1 to newlist  ENDIF  IF the first item in list1<the first item in list2  THEN  Remove the first item from list1 and add it to newlist  ELSE  Remove the first item from list2 and add it to newlist  ENDIF  ENDWHILE  IF list1 is empty THEN  Add the reminder of LIST2 to newlist  ELSE  ADD the remainder of list1 to newlist  ENDIF

BACFEDHG BACFE DH G AB CF DEGH AB CF DEGH ABCDEFGH

Quick sort: pick an item and call it the pivot, normally the first item is picked. Split the remainder of the list into two sub-lists where list 1 less than or equal to the pivot and list 2 greater than the pivot. Keep applying the split until the pivot can be combined and sorted.

Quick sort  Place leftPointer at first item in the list and rightPointer at the last item in the list.  WHILE leftPOINTER!=rightPOINTER  WHILE list[leftPointer] < list[rightPointer] AND leftPointer != rightPointer  Add one to leftPointer  END WHILE  Swap list[leftPointer] with list[[rightPointer]  END WHILE  Place leftPointer at first item in the list and rightPointer at the last item in the list.  WHILE leftPOINTER!=rightPOINTER  WHILE list[leftPointer] < list[rightPointer] AND leftPointer != rightPointer  Add one to leftPointer  END WHILE  Swap list[leftPointer] with list[[rightPointer]  END WHILE

CFDEAB AB CFDE PIVOT ACB D E F D E F ACB ABCDEF SUBLIST

Questions  In quick sort, a pivot is picked. Explain what this pivot is used for. 149  Describe what is checked during the feasibility study152  Describe what is meant by user documentation  In quick sort, a pivot is picked. Explain what this pivot is used for. 149  Describe what is checked during the feasibility study152  Describe what is meant by user documentation