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Efficient Times Table Generator Design

Learn loops, FOR loop usage, nesting loops, loop design in QBasic. Create a program to display times tables based on user input. Understand the concept of iteration and repetition in programming.

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Efficient Times Table Generator Design

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  1. CP1020 - Week 6 Repetition

  2. Aims and Objectives • Understand what loops are and why they are needed • Understand the FOR loop used in programming • Understand the concept of nesting loops and why they may be necessary • Be able to design and codeloops in QBasic

  3. The Three Main Programming Constructs • So far we have looked at: • Sequence - the ordering of program statements INPUT “the wholesale cost of the article”; fCost LET fRetail = 2 * fCost PRINT “the retail cost of the article is ”; fRetail • Selection - making decisions in our code If...Then...Else... If...Then...Elseif... Select...Case

  4. Repetition • We can now introduce the third construct: • Iteration - looping or repetition • allows one or more statements to be repeated either a fixed number of times or until a particular condition(s) is satisfied

  5. Count Down Loop If Problem THEN Abort Else Ignite rocket Disconnect From Launch Pad

  6. Times Table Problem A program is required to display the times table for a number inputted by the user. • Suppose the number inputted was 6, the program should then generate the 6 times table as follows: 1 x 6 is 6 2 x 6 is 12 3 x 6 is 18 etc... 11 x 6 is 66 12 x 6 is 72

  7. Times Table Initial Design • Based only on what we have done so far:1 Read value in from keyboard2 Display times table for value entered3 End program • This looks OK, but let’s expand step 2...

  8. Times Table Expanded Design • 1 Read value in from keyboard2 Display times table for value entered2.1 Display title2.2 Display 1 * value entered2.3 Display 2 * value entered2.4 Display 3 * value entered2.5 Display 4 * value entered2.6 Display 5 * value entered2.7 Display 6 * value entered

  9. Times table continued 2.8 Display 7 * value entered2.9 Display 8 * value entered2.10 Display 9 * value entered2.11 Display 10 * value entered2.12 Display 11 * value entered2.13 Display 12 * value entered 3 End program

  10. Times Table Code • Code for the long winded solution: DIM iTimes AS INTEGERINPUT iTimes PRINT "The "; iTimes; " Times Table"PRINT "1 * "; iTimes; " = "; 1 * iTimesPRINT "2 * "; iTimes; " = "; 2 * iTimesPRINT "3 * "; iTimes; " = "; 3 * iTimesPRINT "4 * "; iTimes; " = "; 4 * iTimesPRINT "5 * "; iTimes; " = "; 5 * iTimesPRINT "6 * "; iTimes; " = "; 6 * iTimesPRINT "7 * "; iTimes; " = "; 7 * iTimes

  11. Times table problem • PRINT "8 * "; iTimes; " = "; 8 * iTimesPRINT "9 * "; iTimes; " = "; 9 * iTimesPRINT "10 * "; iTimes; " = "; 10 * iTimesPRINT "11 * "; iTimes; " = "; 11 * iTimesPRINT "12 * "; iTimes; " = "; 12 * iTimesEND • Clearly this is very tedious and becomes unworkable as the number of repeat task increases • However I have cunning plan!

  12. Times Table Looping Design • A new design, this time using a For...Next loop1 Read value in from keyboard2 Display title3 Display times table for value entered3.1 For Counter (1 to 12) 3.1.1 Display Counter X value entered End For 4 End program • This type of loop is used to perform a statement (or set of statements) a fixed number of times • This is ideal for our times table problem

  13. For...Next Loop Construct • The For...Next construct should be used when you know how may times the loop should be executed before entering the loop • General structure:FORCount=StartValueTOEndValue[STEPincrement] statements...NEXT[Count]Count can be any of these types: • Integer or Long • Single or Double

  14. Times Table Looping Code • Code for the looping version of the times table: DIM iCount AS INTEGERDIM iTimes AS INTEGERINPUT iTimes CLSPRINT "The "; iTimes; " Times Table"FOR iCount = 1 TO 12PRINT iCount;" * ";iTimes;" = ";iCount * iTimesNEXT iCountEND E.g. 2 * 6 = 12

  15. 6 Times Table Example Output The 6 times table 1 * 6 = 6 2 * 6 = 12 3 * 6 = 18 4 * 6 = 24 5 * 6 = 30 6 * 6 = 36 7 * 6 = 42 8 * 6 = 48 9 * 6 = 54 10 * 6 = 60 11 * 6 = 66 12 * 6 = 72

  16. For...Next Loop Step • We can also specify the step size and count backwards:DIM iCount AS INTEGERFOR iCount = 100 TO 0 STEP -10PRINT "iCount = "; iCountNEXT iCountEND SUB • Unless a STEP is specified the For loopwill increment by 1 each time • You should never change the value ofthe control variable(iCount) inside the For loop

  17. Nesting Loops • Consider the following:A program is required to print out the full 12 times table • A typical screen could be as follows: 1 times table 1 2 3 4 5 6 7 8 9 10 11 12 2 times table 2 4 6 8 10 12 14 16 1 8 20 22 24 3 times table 3 6 9 12 15 18 21 24 27 30 33 36 4 times table 4 8 12 16 20 24 28 32 36 40 44 48 5 times table 5 10 15 20 25 30 35 40 45 50 55 60 6 times table 6 12 18 24 30 36 42 48 54 60 66 72 and so on……...

  18. Design For Full Times Tables Step1 For RowCounter (1 to 12) 1.1 For ColumnCounter (1 to 12) Do1.1.1 Display RowCounter x ColumnCounter End For1.2 Display a new line End For 2 End program

  19. Coding DIM iRowCount AS INTEGER ‘line counterDIM iColumnCount AS INTEGER ‘item on line counterCLSFOR iRowCount = 1 TO 12PRINT iRowCount; "Times table: ";FOR iColumnCount = 1 TO 12PRINT iColumnCount * iRowCount;NEXT iColumnCountPRINTNEXT iRowCountEND

  20. Questions 1 When would you use a For loop? 2 What will the output from the following code be? For iRow = 6 To 4 Step -1 For iCol = -3 To 1 Step 2 Print iRow; " * "; iCol; " = "; iRow * iCol Next iCol Print Next iRow Return to view another lecture

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