7.1-7.7 computing

• Program development life cycle


  1. Analysis

  2. Design

  3. Coding and iterative testing

  4. Testing completed program
• Analysis


  1. Define the problem

  2. Investigate the current system if there is one

  3. Plan a solution
• Design


  1. Design the solution in detail now that you have the solution in mind

  2. Create structure diagrams / Flowcharts / Pseudocode to represent the system
• Coding and iterative testing


  Write the code and actually develop the new system
• Testing completed program


  Thoroughly test the completed coded version
• Sequence


  A number of steps are performed one after another. Sometimes the order matters, sometimes it doesn't.
• Selection


  Used to choose a particular path , and carry out only certain actions
• Selection constructs


  • IF…THEN…ENDIF
  • CASE OF…OTHERWISE…ENDCASE
• Repetition


  • FOR…TO…NEXT → Repeats a set number of times
  • REPEAT…UNTIL → Number of repeats is unknown, completed at least once. (condition after)
  • WHILE…DO…ENDWHILE → Number of repeats unknown, may never be completed. (condition before)
• Totalling


  It keeps a running total of values in a program, done by changing a variable (total ← total + StudentMark)
• Counting


  Keeps a running count of how many times something happens, done by changing a variable (Passcount ← Passcount + 1)
• Average


  Calculates mean, totalling and counting are used. (sum of all values/number of values)
• Maximum


  IFMark[3]> MaxMark THEN MaxMark ← Mark[3]
• Minimum


  If Mark[5] < MinMark THEN MinMark ← Mark [5]
• Linear search


  Iterate across the array left to right, searching for a specified element
• Linear search


  1. Repeat starting at the first element

  2. If the first element is what you're looking for, stop

  3. Otherwise, move to the next element
• Bubble sort


  It is used to sort data (From smallest to biggest or from biggest to smallest)
• Test data


  Once a computer program has been completed and coding & iterative testing has been carried out, a program should be thoroughly tested in every circumstance to ensure the software meets expectations
• Normal test data


  Normal data is test data that is expected and should be accepted by the system. Normal test data is simply used to test whether or not a program is functioning correctly when typical / normal data is entered.
• Example normal test data

  • It asks you to input an integer between 0 and 100 and you input 55
• Abnormal test data


  Computer programs should also be tested to see if they behave correctly when data that is NOT what is expected is entered by the user.
• Example abnormal test data

  • It asks you to input an integer between 0 and 100 and you input -3 or six
• Extreme test data


  Extreme data is test data at the upper or lower limits of expectations that should be accepted by the system. Extreme values are still normal data. However, the values are chosen to be at the absolute limits of the normal range.
• Extreme test data


  • In the example of a program to accept percentage marks, extreme test data would be 0 and 100
• Boundary test data


  Boundary data is a pair of test data values at each end of a range. This data is a combination of the extreme values which should be accepted, and abnormal data which are the immediate values before or beyond the limits of expectations that should be rejected.
• Boundary test data

  • In the example of a program designed to provide an average of percentage marks, the boundary test data would be: Lower range: -1, 0 Upper range: 101, 100
• Validation


  Aims to make sure that data is sensible, reasonable, complete and within acceptable boundaries
• Types of validation checks


  • Range checks
  • Length checks
  • Type checks
  • Presence checks
  • Format checks
  • Check digits
• Range check


  Checks that the value of a number is between an upper value and a lower value
• Length check


  Checks either that data contains an exact number of characters or that the data entered is a reasonable number of characters
• Type check


  Checks that the data entered is of a given data type
• Presence check


  Checks to ensure that some data has been entered and the value has not been left blank
• Format check


  Checks that the characters entered conform to a pre-defined pattern
• Check digit


  The final digit included in a code, calculated from all the other digits in the code, used to identify errors in data entry
• Verification


  Checking that the data on the original source document is identical to the data that has been entered into the system or object document
• Verification methods for input data


  • Double entry
  • Screen/visual check
• Double entry(verification)


  The data is entered twice, sometimes by different operators, and the computer system compares both entries and outputs an error message if they are different
• visual check(verification)


  A manual check completed by the user who is entering the data, where the data is displayed on the screen and the user is asked to confirm that it is correct before continuing
• Validation


  Aims to make sure that data is sensible, reasonable, complete and within acceptable boundaries
• Types of validation checks

  • Range checks
  • Length checks
  • Type checks
  • Presence checks
  • Format checks
  • Check digits