Visual C++ Programming: Concepts and Projects

1. Visual C++ Programming: Concepts and Projects Chapter 5A: Repetition (Concepts)

2. Objectives In this chapter, you will: • Learn the strengths and weaknesses of user-controlled repetition • Study the various forms of repetition control structures • Learn how pre- and post-test loops work • Use for loops, while loops, and do...while loops Programming with Visual C++

3. Objectives (continued) • Generate random numbers • Learn how the loop process relates to summation, counting, and other common tasks • Use a loop to construct an extended string of characters Programming with Visual C++

4. User-Controlled Repetition • Forms of repetition • The user can be required to repeat tasks (user-controlled repetition) • The program can repeat tasks automatically • User-controlled repetition relies on the user to perform repeated actions • Entering data into text boxes • Clicking buttons Programming with Visual C++

5. User-Controlled Repetition (continued) • The need for user-controlled repetition • Consider a program that requires the user to enter five numbers into five TextBoxes • This program is difficult to revise to accommodate more or fewer values • For example: Revising it to accommodate 15 data values requires 15 TextBoxes • How can the program be redesigned so that the user can enter any number of values? Programming with Visual C++

6. User-Controlled Repetition (continued) Programming with Visual C++

7. User-Controlled Repetition (continued) Programming with Visual C++

8. User-Controlled Repetition (continued) • This program is difficult to revise to accommodate more or fewer values • For example: Revising it to accommodate 15 data values requires 15 TextBoxes and lots of additional code Programming with Visual C++

9. User-Controlled Repetition (continued) Programming with Visual C++

10. Programming with Visual C++

11. User-Controlled Repetition (continued) • The problem with the previous approach was that each program was a single-purpose solution • Designed to solve specific instances of a problem • Single-purpose solution • Works only with one set of input values • Must undergo extensive revision whenever the terms of the problem change (more input values) • What is needed is a general-purpose solution • Works with any number of input values • General averaging program • Uses user-controlled repetition • Handles any amount of input • Very few variables and interface controls • No need to change it to accommodate more data Programming with Visual C++

12. User-Controlled Repetition (continued) • A general averaging program • Uses user-controlled repetition • Handles any amount of input • Very few variables and interface controls • No need to change it to accommodate more data • Users enter one data value at a time • Clicking the “Add To Sum” button adds the value to the sum and calculates and displays additional statistics Programming with Visual C++

13. User-Controlled Repetition (continued) Programming with Visual C++

14. User-Controlled Repetition (continued) • The program accommodates five, 15, or any number of data values without modification • After entering multiple data values, the results are displayed • For example: The next slide indicates the result after the values 23, 34, 41, 37, and 19 have been entered Programming with Visual C++

15. User-Controlled Repetition (continued) Programming with Visual C++

16. User-Controlled Repetition (continued) • The general approach requires only one variable to store data (num) • The sum of the multiple data entries is “accumulated” over the course of user interaction Programming with Visual C++

17. Accumulating a Sum and Counting • Summation is the process of adding values to arrive at a sum • Accumulating a sum • A sum can be accumulated one addition at a time in a repetitive process • Counting • A process in which the value 1 is added to a counter in a repetitive process Programming with Visual C++

18. Instance Variables • Summation and counting require variables that remain in scope after a method (such as a Click()event) ends • Variable scope refers to the visibility of a variable to a program • Local scope • The variable is declared in an event handler • The variable exists only within that event handler • The variable can be processed only by statements in that event handler • Class scope • The variable is declared within the Form1 class but outside of all event handlers • Every event handler can use it • Variables with class scope are called instance variables Programming with Visual C++

19. Programming with Visual C++

20. Instance Variables (continued) • Instance variables are declared • Immediately after the line #pragma endregion • Outside of all event handlers • Instance variables are required for summation or counting • They are initialized to 0 by default when declared • Example: sum, count • Each time the user clicks the button, a value is added to the sum and 1 is added to the count Programming with Visual C++

21. Programming with Visual C++

22. Instance Variables (continued) • Instance variables make a general solution to the summation program possible • The sum retains its value from one Click() event call to the next • The users are in control • As long as they repeat the process of entering data and clicking the button, their data value will be added to the sum Programming with Visual C++

23. Repetition Control Structures • Repetition may also be performed automatically, without the user’s participation • Repetition control structures (loops) allow your program to automatically repeat one or more statements • Characteristics of all loops • Loop condition • Boolean expression that must be true for the loop to continue • Loop control variable • A variable evaluated by the loop condition • Loop body • The statements in a loop • Iteration • A complete pass through the loop body statements Programming with Visual C++

24. Repetition Control Structures (continued) • Types of loops • Pre-test loop • Loop condition comes before loop body • Post-test loop • Loop condition comes after the loop body Programming with Visual C++

25. Repetition Control Structures (continued) Programming with Visual C++

26. The while Loop • A pre-test loop • Repetition of the loop body continues as long as the pre-test evaluates to true • Repetition stops when the pre-test evaluates to false • Control transfers to the next statement after the loop Programming with Visual C++

27. The while Loop (continued) Programming with Visual C++

28. The while Loop (continued) • Keyword while, followed by a loop condition and then the loop body Programming with Visual C++

29. The while Loop (continued) • This while loop adds up the sum of all integers from 50 to 99 Programming with Visual C++

30. The while Loop (continued) • Incrementation • Adding 1 to a loop control variable • Shorthand version: num += 1; • Prefix incrementation: ++num; • Postfix incrementation: num++; Programming with Visual C++

31. The while Loop (continued) • If num was initially set to 50, this loop accumulates the sum of all integers from 50 to 99 • num is added to sum and then num is incremented Programming with Visual C++

32. The while Loop (continued) • Decrementation • Subtracting 1 from a loop control variable • Shorthand version: num -= 1; • Prefix decrementation: --num; • Postfix decrementation: num--; Programming with Visual C++

33. do…while Loops • Post-test loop condition • Repetition of the loop body continues as long as the post-test evaluates to true • Repetition stops and control is transferred to the first statement after the loop when the post-test evaluates to false Programming with Visual C++

34. do…while Loops (continued) Programming with Visual C++

35. do…while Loops • do … whilesyntax • Keyword do at top of loop • Followed by loop body • Then keyword while • Followed by the loop condition Programming with Visual C++

36. do…while Loops (continued) • This do…while loop accumulates the sum of all integers from 50 to 99 Programming with Visual C++

37. The for Loop • Pre-test loop • Built-in loop control variable that often serves as a counter • Often called “counter-controlled” loops Programming with Visual C++

38. The for Loop (continued) Programming with Visual C++

39. The for Loop (continued) • Three clauses after the for statement • Initialization of loop control variable • Pre-test condition • Update of loop control variable Programming with Visual C++

40. The for Loop (continued) Programming with Visual C++

41. The for Loop • The initialization clause is executed only once, when the loop is first encountered • The update clause is executed at the end of each iteration, prior to the pre-test evaluation • This example adds up all the values from 1 to 5 Programming with Visual C++

42. Common Loop Tasks • Formula translation • Accumulating a product • Building a string • Generating random numbers • Finding the largest/smallest value • Counting specific values • Nested loops Programming with Visual C++

43. Formula Translation • Summation • Initial value • Terminal value • Summation process • Can easily be translated from mathematical symbols into C++ code Programming with Visual C++

44. Formula Translation (continued) Programming with Visual C++

45. Formula Translation (continued) Programming with Visual C++

46. Accumulating a Product • Like summation only with multiplication • Factorial number (!) example • Definition: 0! = 1, 1! = 1, n! = n x (n-1)! • 5! Is 5 x 4 x 3 x 2 x 1 • Initialize the product to 1 outside of the loop Programming with Visual C++

47. Building a String • Repeat the process of adding a new character to a String variable within the loop body • Declare an empty string outside the loop • Add a new character to it with each iteration • Concatenating characters • Uses regular (+) or shorthand (+=) concatenation operator • Conversion to String type is implicit (ToString()is not required) Programming with Visual C++

48. Building a String (continued) Programming with Visual C++

49. Generating Random Numbers • A random number • Is selected from a range of values • Each value has the same likelihood of selection • Requires random number object derived from the system-defined Random class • Random number generation should start from a unique value each time the program runs • Use DateTime variable now.Milliseconds to capture milliseconds since midnight (a unique value) • Next()method generates an integer within a specified range • Two parameters (first, last) • The value will be any integer from first up to (but not including) last Programming with Visual C++

50. Generating Random Numbers (continued) Programming with Visual C++