Repeating Instructions

1. 6 Repeating Instructions C# Programming: From Problem Analysis to Program Design 3rd Edition C# Programming: From Problem Analysis to Program Design

2. Part II C# Programming: From Problem Analysis to Program Design

3. For Loop • Pretest form of loop (like the while) • Considered specialized form of while statement • Usually associated with counter-controlled types • Packages initialization, test, and update all on one line • General form is: for (statement; conditional expression; statement) statement; • Interpreted as: for (initialize; test; update) statement; C# Programming: From Problem Analysis to Program Design

4. For Loop (continued) Figure 6-8 Flow of control with a for statement C# Programming: From Problem Analysis to Program Design

5. For Loop (continued) For loop is executed as shown in the numbered steps Figure 6-9 Step of the for statement C# Programming: From Problem Analysis to Program Design

6. Comparison of While and For Statement int counter = 0; while (counter < 11) { Console.WriteLine("{0}\t{1}\t{2}", counter, Math.Pow(counter,2), Math.Pow(counter,3)); counter++; } for (int counter = 0; counter < 11; counter++) { Console.WriteLine("{0}\t{1}\t{2}", counter, Math.Pow(counter,2), Math.Pow(counter,3)); } Replace above while loop with for loop below –does same C# Programming: From Problem Analysis to Program Design

7. For Loop (continued) counter out of SCOPE Figure 6-10 Syntax error C# Programming: From Problem Analysis to Program Design

8. Ways to Initialize, Test, and Update For Statements • for (int counter = 0, val1 = 10; counter < val1; counter++) • for ( ; counter < 100; counter+=10) // No initialization • for (int j = 0; ; j++) // No conditional expression • for ( ; j < 10; counter++, j += 3) // Compound update • for (int aNum = 0; aNum < 101; sum += aNum, aNum++) ; // Null loop body • for (int j = 0,k = 10; j < 10 && k > 0; counter++, j += 3) C# Programming: From Problem Analysis to Program Design

9. Ways to Initialize, Test, and Update For Statements (continued) • Floating-point variables can be used • for initialization, expressions, and update for (double d = 15.0; d < 20.0; d += 0.5) { Console.Write(d + “\t”); } • The output produced 15 15.5 16 16.5 17 17.5 18 18.5 19 19.5 C# Programming: From Problem Analysis to Program Design

10. Ways to Initialize, Test, and Update For Statements (continued) • Can change the loop control variable inside the loop for (double d = 15.0; d < 20.0; d += 0.5) { Console.Write(d + “\t”); d += 2.0 } • The output produced 15 17.5 C# lets you change the conditional expressionendValue inside the loop body– BUT, be careful here C# Programming: From Problem Analysis to Program Design

11. Foreach Statement • Used to iterate or move through a collection • Array (Chapter 7) • General form • foreach (type identifier in expression) • statement; • Expression is the collection (array) • Type is the kind of values found in the array • Restriction on foreach—cannot change values • Access to the elements is read-only C# Programming: From Problem Analysis to Program Design

12. Do…While Statements • Posttest • General form do { statement; } while ( conditional expression); Figure 6-12 Do…while loop C# Programming: From Problem Analysis to Program Design

13. Do…While Example • int counter = 10; • do // No semicolon on this line • { • Console.WriteLine(counter + "\t" + Math.Pow(counter, 2)); • counter--; • } • while (counter > 6); • The output of this code is: • 10 100 • 9 81 • 8 64 • 7 49 C# Programming: From Problem Analysis to Program Design

14. Nested Loops • Loop can be nested inside an outer loop • Inner nested loop is totally completed before the outside loop is tested a second time int inner; for (int outer = 0; outer < 3; outer++) { for(inner = 10; inner > 5; inner --) { Console.WriteLine("Outer: {0}\tInner: {1}", outer, inner); } } 15 lines printed C# Programming: From Problem Analysis to Program Design

15. Recursion • Technique where a method calls itself repeatedly until it arrives at the solution • Algorithm has to be developed so as to avoid an infinite loop • To write a recursive solution, an algorithm has to be developed so as to avoid an infinite loop • Have to identify a base case • Base case is the simplest form of the solution C# Programming: From Problem Analysis to Program Design

16. Recursive Call Figure 6-15 Recursive evaluation of n! C# Programming: From Problem Analysis to Program Design

17. Unconditional Transfer of Control • Break • Used with switch statement • Place in the body of a loop to provide immediate exit • Be careful (Single Entry/Single Exit) • Continue • When reached, a new iteration of the nearest enclosing while, do…while, for, or foreach statement is started • Other jump statements • goto, throw, and return • Use sparingly C# Programming: From Problem Analysis to Program Design

18. Deciding Which Loop to Use • Sometimes a personal choice • Body of the do…while always executed at least once • Posttest type • Numeric variable being changed by a consistent amount– for statement • While statement can be used to write any type of loop • Pretest type C# Programming: From Problem Analysis to Program Design

19. LoanApplication Example Figure 6-16 Problem specification for the LoanApplication example C# Programming: From Problem Analysis to Program Design

20. LoanApplication Example (continued) C# Programming: From Problem Analysis to Program Design

21. LoanApplicationExample(continued) Figure 6-17 Prototype for the LoanApplication example C# Programming: From Problem Analysis to Program Design

22. LoanApplicationExample(continued) Figure 6-18 Class diagrams C# Programming: From Problem Analysis to Program Design

23. Formulas Used for LoanApplication Example C# Programming: From Problem Analysis to Program Design

24. Properties for LoanApplication Example C# Programming: From Problem Analysis to Program Design

25. Pseudocode –Loan Class Figure 6-19 Behavior of Loan class methods C# Programming: From Problem Analysis to Program Design

26. Pseudocode – LoanApp Class Figure 6-20 Behavior of LoanApp class methods C# Programming: From Problem Analysis to Program Design

27. Desk Check of LoanApplication Example C# Programming: From Problem Analysis to Program Design

28. /* Loan.cs * Creates fields for the amount of loan, interest rate, and number of years. * Calculates amount of payment and produces an amortization schedule. */ using System; using System.Windows.Forms; namespace Loan { publicclass Loan { privatedouble loanAmount; privatedouble rate; privateint numPayments; privatedouble balance; privatedouble totalInterestPaid; privatedouble paymentAmount; privatedouble principal; privatedouble monthInterest; Loan class C# Programming: From Problem Analysis to Program Design

29. // Constructors public Loan( ) { } public Loan(double loan, double interestRate, int years) { loanAmount = loan; if( interestRate < 1) rate = interestRate; else // In case directions aren't followed rate = interestRate / 100; // convert to decimal numPayments = 12 * years; totalInterestPaid = 0; } // Property accessing payment amount publicdouble PaymentAmount { get { return paymentAmount; } } C# Programming: From Problem Analysis to Program Design

30. // Remaining properties defined for each fields as shown on Slide #50 // Determine payment amount based on number of years, // loan amount, and rate publicvoid DeterminePaymentAmount( ) { double term; term = Math.Pow((1 + rate / 12.0), numPayments); paymentAmount = ( loanAmount * rate / 12.0 * term) / (term - 1.0); } // Returns a string containing an amortization table publicstring ReturnAmortizationSchedule() { string aSchedule = "Month\tInt.\tPrin.\tNew"; aSchedule += "\nNo.\tPd.\tPd.\tBalance\n"; balance = loanAmount; C# Programming: From Problem Analysis to Program Design

31. for (int month = 1; month <= numPayments; month++) { CalculateMonthCharges(month, numPayments); aSchedule += month + "\t“ + monthInterest.ToString("F") + "\t“ + principal.ToString("F") + "\t" + balance.ToString("C") + "\n"; } return aSchedule; } // Calculates monthly interest and new balance publicvoid CalculateMonthCharges(int month, int numPayments) { double payment = paymentAmount; monthInterest = rate / 12 * balance; C# Programming: From Problem Analysis to Program Design

32. if (month == numPayments) { principal = balance; payment = balance + monthInterest; } else { principal = payment - monthInterest; } balance -= principal; } // Calculates interest paid over the life of the loan publicvoid DetermineTotalInterestPaid( ) { totalInterestPaid = 0; balance = loanAmount; C# Programming: From Problem Analysis to Program Design

33. for (int month = 1; month <= numPayments; month++) { CalculateMonthCharges(month, numPayments); totalInterestPaid += monthInterest; } } } } C# Programming: From Problem Analysis to Program Design

34. /* LoanApp.cs * Used for testing Loan class. Prompts user for input values. * Calls method to display payment amount and amortization * schedule. Allows more than one loan calculation. */ using System; using System.Windows.Forms; namespace Loan { class LoanApp { staticvoid Main( ) { int years; double loanAmount; double interestRate; string inValue; char anotherLoan = 'N'; LoanApp class C# Programming: From Problem Analysis to Program Design

35. do { GetInputValues(out loanAmount, out interestRate, out years); Loan ln = new Loan(loanAmount, interestRate, years); ln.DeterminePaymentAmount( ); Console.WriteLine( ); Console.WriteLine(ln.ReturnAmortizationSchedule()); ln.DetermineTotalInterestPaid( ); Console.WriteLine("Payment Amount: {0:C}", ln.PaymentAmount); Console.WriteLine("Interest Paid over Life of Loan: " + ln.TotalInterestPaid); Console.Write("Do another Calculation? (Y or N)"); inValue = Console.ReadLine( ); anotherLoan = Convert.ToChar(inValue); } while ((anotherLoan == 'Y')|| (anotherLoan == 'y')); } C# Programming: From Problem Analysis to Program Design

36. // Prompts user for loan data staticvoid GetInputValues(outdouble loanAmount, outdouble interestRate, outint years) { string sValue; Console.Write("Loan Amount: "); sValue = Console.ReadLine( ); loanAmount = Convert.ToDouble(sValue); Console.Write("Interest Rate (as a decimal value): "); sValue = Console.ReadLine( ); interestRate = Convert.ToDouble(sValue); Console.Write("Number of Years to Finance: "); sValue = Console.ReadLine( ); years = Convert.ToInt32(sValue); } } } C# Programming: From Problem Analysis to Program Design

37. LoanApplication Example Figure 6-21 LoanApplication output C# Programming: From Problem Analysis to Program Design

38. Coding Standards • Guidelines for Placement of Curly Braces • Spacing Conventions • Advanced Loop Statement Suggestions C# Programming: From Problem Analysis to Program Design

39. Chapter Summary • Major strengths of programming languages attributed to loops • Types of loops • while • Counter-controlled • State-controlled • Sentinel-controlled • for • foreach • do…while C# Programming: From Problem Analysis to Program Design

40. Chapter Summary (continued) • Conditional expressions used with loops • Nested loops • Unconditional transfer of control • Which use loop structures? • Loop structures for different types of applications C# Programming: From Problem Analysis to Program Design