BCS - Software Engineering - Short note04092015.docx

Dry Run

•        You can test your program without using a computer by dry running it on paper

•        You act as the computer – following the instructions of the program, recording the valves of the variables at each stage

•        You can do this with a table

•        The table with have column headed with the names of the variables in the program

•        Each row in the table will be labelled with a line number form the program.

•        The entries of each row in th e table will be values of the variables after the execution of the statement on that line

•        You don’t need a row for every line in the program, just those lines where some significant change to the state of the program occurs e.g a variable gets a new value

•        In this table you can record all relevant changes to the variables as the program progresses, thereby test the logic of the program / algorithm

•        Do a dry run before you code your program on computer this way any logic errors will come to light during the dry run

•        L1  Declare two variables , first num second num

•        L2  Initialise both variables to 0

•        L3  first num = 0 second num = 0

•        L4  Ask user to enter first number

•        L5  Assign user input to first num variable  

•        L6  Ask user to enter second number

•        L7  Assign user input to second num variable

•        L8  Add first num to second num

•        L9  Print result

•        Do a Dry run for this program assuming the user enters 17 for first number and 24 for the second

After execution	First num	Second num	Result
Line 2	0	0
Line 5	17	0
Line 7	17	24
Line 8	17	24	41

White box testing

1.      White-box testing (also known as clear box testing, glass box testing, transparent box testing, and structural testing) is a method of testing software that tests internal structures or workings of an application, as opposed to its functionality (i.e. black-box testing).

2.       

3.      The Differences Between Black Box Testing and White Box Testing are listed below.

4.       

Criteria	Black Box Testing	White Box Testing
Definition	Black Box Testing is a software testing method in which the internal structure/ design/ implementation of the item being tested is NOT known to the tester	White Box Testing is a software testing method in which the internal structure/ design/ implementation of the item being tested is known to the tester.
Levels Applicable To	Mainly applicable to higher levels of testing:Acceptance Testing System Testing	Mainly applicable to lower levels of testing:Unit Testing Integration Testing
Responsibility	Generally, independent Software Testers	Generally, Software Developers
Programming Knowledge	Not Required	Required
Implementation Knowledge	Not Required	Required
Basis for Test Cases	Requirement Specifications	Detail Design

Sorting algorithms

·        Sorting Arrays
    Bubble Sort
   Exchange Sort
   Selection Sort
   Insertion Sort
 

	Bubble Sort In the bubble sort, as elements are sorted they gradually "bubble" (or rise) to their proper location in the array, like bubbles rising in a glass of soda. The bubble sort repeatedly compares adjacent elements of an array. The first and second elements are compared and swapped if out of order.  Then the second and third elements are compared and swapped if out of order.  This sorting process continues until the last two elements of the array are compared and swapped if out of order. When this first pass through the array is complete, the bubble sort returns to elements one and two and starts the process all over again.  So, when does it stop?  The bubble sort knows that it is finished when it examines the entire array and no "swaps" are needed (thus the list is in proper order).  The bubble sort keeps track of the occurring swaps by the use of a flag. The table below follows an array of numbers before, during, and after a bubble sort fordescending order.  A "pass" is defined as one full trip through the array comparing and if necessary, swapping, adjacent elements.  Several passes have to be made through the array before it is finally sorted.    Array at beginning:  84 69 76 86 94 91 After Pass #1: 84 76 86 94 91 69 After Pass #2:  84 86 94 91 76 69 After Pass #3:  86 94 91 84 76 69 After Pass #4:  94 91 86 84 76 69 After Pass #5 (done):  94 91 86 84 76 69 The bubble sort is an easy algorithm to program, but it is slower than many other sorts.  With a bubble sort, it is always necessary to make one final "pass" through the array to check to see that no swaps are made to ensure that the process is finished.
	Exchange Sort   The exchange sort is similar to its cousin, the bubble sort, in that it compares elements of the array and swaps those that are out of order.  (Some people refer to the "exchange sort" as a "bubble sort".)  The difference between these two sorts is the manner in which they compare the elements. The exchange sort compares the first element with each following element of the array, making any necessary swaps.    When the first pass through the array is complete, the exchange sort then takes the second element and compares it with each following element of the array swapping elements that are out of order.  This sorting process continues until the entire array is ordered. Let's examine our same table of elements again using an exchange sort for descending order.  Remember, a "pass" is defined as one full trip through the array comparing and if necessary, swapping elements Array at beginning:  84 69 76 86 94 91 After Pass #1: 94 69 76 84 86 91 After Pass #2: 94 91 69 76 84 86 After Pass #3:  94 91 86 69 76 84 After Pass #4:  94 91 86 84 69 76 After Pass #5 (done):  94 91 86 84 76 69
Selection Sort The selection sort is a combination of searching and sorting. During each pass, the unsorted element with the smallest (or largest) value is moved to its proper position in the array.  The number of times the sort passes through the array is one less than the number of items in the array.  In the selection sort, the inner loop finds the next smallest (or largest) value and the outer loop places that value into its proper location. Let's look at our same table of elements using a selection sort for descending order.  Remember, a "pass" is defined as one full trip through the array comparing and if necessary, swapping  elements. Array at beginning:  84 69 76 86 94 91 After Pass #1: 84 91 76 86 94 69 After Pass #2: 84 91 94 86 76 69 After Pass #3:  86 91 94 84 76 69 After Pass #4:  94 91 86 84 76 69 After Pass #5 (done):  94 91 86 84 76 69
Insertion Sort The insertion sort, unlike the other sorts, passes through the array only once.  The insertion sort is commonly compared to organizing a handful of playing cards.  You pick up the random cards one at a time.  As you pick up each card, you insert it into its correct position in your hand of organized cards.  The insertion sort splits an array into two sub-arrays. The first sub-array (like the cards in your hand) is always sorted and increases in size as the sort continues. The second sub-array (like the cards to be picked up) is unsorted, contains all the elements yet to be inserted into the first sub-array, and decreases in size as the sort continues.   Let's look at our same example using the insertion sort for descending order.   Array at beginning:  84 69 76 86 94 91 = 1st sub-array 84 69 76 86 94 91 = 2nd sub-array 84 69 76 86 94 91 84 76 69 86 94 91 86 84 76 69 94 91 94 86 84 76 69 91 2nd sub-array empty 94 91 86 84 76 69 The insertion sort maintains the two sub-arrays within the same array.  At the beginning of the sort, the first element of the first sub-array is considered the "sorted array".  With each pass through the loop, the next element in the unsorted second sub-array is placed into its proper position in the first sorted sub-array. The insertion sort can be very fast and efficient when used with smaller arrays.  Unfortunately, it loses this efficiency when dealing with large amounts of data