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Chapter 5 – Control Structures: Part 2 Outline 5.1 Introduction 5.2 Essentials of Counter-Controlled Repetition 5.3 for Repetition Structure 5.4 Examples Using the for Structure 5.5 switch Multiple-Selection Structure 5.6 do/while Repetition Structure 5.7 Statements break and continue 5.8 Logical and Conditional Operators 5.9 Structured-Programming Summary

5.2 Essentials of Counter Controlled Repetition Counter controlled repetition Control variable The variable used to determine if the loop continues Initial value of the control variable Incrementing/decrementing of the variable The condition When the looping should continue

WhileCounter.cs Program Output 1 // Fig. 5.1: WhileCounter.cs 2 // Counter-controlled repetition. 3 4 using System; 5 6 class WhileCounter 7 { 8 static void Main( string [] args ) 9 { 10 int counter = 1 ; // initialization 11 12 while ( counter <= 5 ) // repetition condition 13 { 14 Console.WriteLine( counter ); 15 counter++; // increment 16 17 } // end while 18 19 } // end method Main 20 21 } // end class WhileCounter 1 2 3 4 5 This is where the counter variable is initialized. It is set to 1. The loop will continue until counter is greater than five (it will stop once it gets to six) The counter is incremented and 1 is added to it

5.3 for Repetition Structure The for repetition structure Syntax: for (Expression1, Expression2, Expression3) Expression1 = names the control variable Can contain several variables Expression2 = loop-continuation condition Expression3 = incrementing/decrementing If Expression1 has several variables, Expression3 must have several variables accordingly ++counter and counter++ are equivalent Variable scope Expression1 can only be used in the body of the for loop When the loop ends the variable expires

5.3 for Repetition Structure Fig. 5.3 Components of a typical for header. for ( int counter = 1; counter <= 5; counter++ ) Initial value of control variable Increment of control variable Control variable name Final value of control variable for keyword Loop-continuation condition

5.3 for Repetition Structure counter++ Establish initial value of control variable. Determine if final value of control variable has been reached. counter <= 10 Console.WriteLine ( counter * 10 ); true false int counter = 1 Body of loop (this may be multiple statements) Increment the control variable. Fig. 5.4 Flowcharting a typical for repetition structure.

ForCounter.cs Program Output 1 // Fig. 5.2: ForCounter.cs 2 // Counter-controlled repetition with the for structure. 3 4 using System; 5 6 class ForCounter 7 { 8 static void Main( string [] args ) 9 { 10 // initialization, repetition condition and incrementing 11 // are all included in the for structure 12 for ( int counter = 1 ; counter <= 5 ; counter++ ) 13 Console.WriteLine( counter ); 14 } 15 } 1 2 3 4 5 This is where the counter variable is initialized. It is set to 1. The loop will continue until counter is greater than five (it will stop once it gets to six) The counter is incremented (1 is added to it)

5.4 Examples Using the for Structure Increment/Decrement When incrementing In most cases < or <= is used When decrementing In most cases > or >= is used Message boxes Buttons OK OKCancel YesNo AbortRetryIgnore YesNoCancel RetryCancel

5.4 Examples Using the for Structure Massages boxes Icons Exclamation Question Error Information Formatting ( variable : format ) Table 5.9 lists some formatting codes

Sum.cs Program Output 1 // Fig. 5.5: Sum.cs 2 // Summation with the for structure. 3 4 using System; 5 using System.Windows.Forms; 6 7 class Sum 8 { 9 static void Main( string [] args ) 10 { 11 int sum = 0 ; 12 13 for ( int number = 2 ; number <= 100 ; number += 2 ) 14 sum += number; 15 16 MessageBox.Show( "The sum is " + sum, 17 "Sum Even Integers from 2 to 100" , 18 MessageBoxButtons. OK , 19 MessageBoxIcon. Information ); 20 21 } // end method Main 22 23 } // end class Sum Argument 4: MessageBox Icon (Optional) Argument 3: OK dialog button. (Optional) Argument 2: Title bar string (Optional) Argument 1: Message to display Displays a message box with an OK button Has the message box contain an information icon The counter. It is initialized to 2 Once the number is greater than 100 the loop breaks Increments number by 2 every time the loop starts over The caption of the message box The title of the message box

5.4 Examples Using the for Structure

Interest.cs 1 // Fig. 5.8: Interest.cs 2 // Calculating compound interest. 3 4 using System; 5 using System.Windows.Forms; 6 7 class Interest 8 { 9 static void Main( string [] args ) 10 { 11 decimal amount, principal = ( decimal ) 1000.00 ; 12 double rate = .05 ; 13 string output; 14 15 output = "Year\tAmount on deposit\n" ; 16 17 for ( int year = 1 ; year <= 10 ; year++ ) 18 { 19 amount = principal * 20 ( decimal ) Math.Pow( 1.0 + rate, year ); 21 22 output += year + "\t" + 23 String.Format( "{0:C}" , amount ) + "\n" ; 24 } 25 26 MessageBox.Show( output, "Compound Interest" , 27 MessageBoxButtons. OK , MessageBoxIcon. Information ); 28 29 } // end method Main 30 31 } // end class Interest Creates a message box that displays the output with a title of “Compound Interest” has an OK button and an information icon Loops through 10 times starting at 1 and ending at 10, adding 1 to the counter (year) each time Insert a Tab Formats amount to have a currency formatting ($0.00)

5.5 switch Multiple-Selection Structure The switch statement Constant expressions String Integral Cases Case ‘ x ’ : Use of constant variable cases Empty cases The default case The break statement Exit the switch statement

SwitchTest.cs 1 // Fig. 5.10: SwitchTest.cs 2 // Counting letter grades. 3 4 using System; 5 6 class SwitchTest 7 { 8 static void Main( string [] args ) 9 { 10 char grade; // one grade 11 int aCount = 0 , // number of As 12 bCount = 0 , // number of Bs 13 cCount = 0 , // number of Cs 14 dCount = 0 , // number of Ds 15 fCount = 0 ; // number of Fs 16 17 for ( int i = 1 ; i <= 10 ; i++ ) 18 { 19 Console.Write( "Enter a letter grade: " ); 20 grade = Char.Parse( Console.ReadLine() ); 21 22 switch ( grade ) 23 { 24 case 'A' : // grade is uppercase A 25 case 'a' : // or lowercase a 26 ++aCount; 27 break ; 28 29 case 'B' : // grade is uppercase B 30 case 'b' : // or lowercase b 31 ++bCount; 32 break ; 33 Each of these variables acts as a counter so they are initialized to zero The start of the switch statement. The grade variable is used as the data to be tested for each case. Prompt the user for a grade and store it into the grade variable case ‘A’ is empty so it is the same as case ‘a’ Both cases add one to aCount The break statement is used to exit the switch statement and not perform the rest of the operations Both case ‘B’ and case ‘b’ add one to the bCount variable A for loop that initializes i to 1, loops 10 times and increments i by one each time

SwitchTest.cs 34 case 'C' : // grade is uppercase C 35 case 'c' : // or lowercase c 36 ++cCount; 37 break ; 38 39 case 'D' : // grade is uppercase D 40 case 'd' : // or lowercase d 41 ++dCount; 42 break ; 43 44 case 'F' : // grade is uppercase F 45 case 'f' : // or lowercase f 46 ++fCount; 47 break ; 48 49 default : // processes all other characters 50 Console.WriteLine( 51 "Incorrect letter grade entered." + 52 "\nGrade not added to totals." ); 53 break ; 54 55 } // end switch 56 57 } // end for 58 59 Console.WriteLine( 60 "\nTotals for each letter grade are:\nA: {0}" + 61 "\nB: {1}\nC: {2}\nD: {3}\nF: {4}" , aCount, bCount, 62 cCount, dCount, fCount ); 63 64 } // end method Main 65 66 } // end class SwitchTest Both cases add 1 to cCount If grade equals D or d add one to dCount Add one to fCount if grade equals F or f If non of the cases are equal to the value of grade then the default case is executed Display the results

SwitchTest.cs Program Output Enter a letter grade: a Enter a letter grade: A Enter a letter grade: c Enter a letter grade: F Enter a letter grade: z Incorrect letter grade entered. Grade not added to totals. Enter a letter grade: D Enter a letter grade: d Enter a letter grade: B Enter a letter grade: a Enter a letter grade: C Totals for each letter grade are: A: 3 B: 1 C: 2 D: 2 F: 1

5.5 switch Multiple-Selection Structure Fig. 5.11 Flowcharting the switch multiple-selection structure. break; case : a case a action(s) true false . . . break; case b action(s) break; false false case : z case z action(s) break; default action(s) true true case : b

5.6 do/while Repetition Structure The while loops vs. the do/while loops Using a while loop Condition is tested The the action is performed Loop could be skipped altogether Using a do/while loop Action is performed Then the loop condition is tested Loop must be run though once Always uses brackets ({) to prevent confusion

DoWhileLoop.cs Program Output 1 // Fig. 5.12: DoWhileLoop.cs 2 // The do/while repetition structure. 3 4 using System; 5 6 class DoWhileLoop 7 { 8 static void Main( string [] args ) 9 { 10 int counter = 1 ; 11 12 do 13 { 14 Console.WriteLine( counter ); 15 counter++; 16 } while ( counter <= 5 ); 17 18 } // end method Main 19 20 } // end class DoWhileLoop 1 2 3 4 5 The counter is initialized to one These actions are performed at least one Continue looping as long as counter is less than 6 The incrementing task

5.6 do/while Repetition Structure Fig. 5.13 Flowcharting the do / while repetition structure. true false action(s) condition

5.7 Statements break and continue Use Used to alter the flow of control The break statement Used to exit a loop early The continue statement Used to skip the rest of the statements and begin the loop at the first statement in the loop Programs can be completed without their usage

BreakTest.cs 1 // Fig. 5.14: BreakTest.cs 2 // Using the break statement in a for structure. 3 4 using System; 5 using System.Windows.Forms; 6 7 class BreakTest 8 { 9 static void Main( string [] args ) 10 { 11 string output = "" ; 12 int count; 13 14 for ( count = 1 ; count <= 10 ; count++ ) 15 { 16 if ( count == 5 ) 17 break ; // skip remaining code in loop 18 // if count == 5 19 20 output += count + " " ; 21 22 } // end for loop 23 24 output += "\nBroke out of loop at count = " + count; 25 26 MessageBox.Show( output, "Demonstrating the break statement" , 27 MessageBoxButtons. OK , MessageBoxIcon. Information ); 28 29 } // end method Main 30 31 } // end class BreakTest Displays a message box the displays the output, has a title of “demonstrating the break statement,” uses an OK button, and displays an information icon A loop that starts at one, goes to ten, and increments by one If count = 5 then break out of the loop Display the last value that the counter was at before it broke

ContinueTest.cs 1 // Fig. 5.15: ContinueTest.cs 2 // Using the continue statement in a for structure. 3 4 using System; 5 using System.Windows.Forms; 6 7 class ContinueTest 8 { 9 static void Main( string [] args ) 10 { 11 string output = "" ; 12 13 for ( int count = 1 ; count <= 10 ; count++ ) 14 { 15 if ( count == 5 ) 16 continue ; // skip remaining code in loop 17 // only if count == 5 18 19 output += count + " " ; 20 } 21 22 output += "\nUsed continue to skip printing 5" ; 23 24 MessageBox.Show( output, "Using the continue statement" , 25 MessageBoxButtons. OK , MessageBoxIcon. Information ); 26 27 } // end method Main 28 29 } // end class ContinueTest A loop that starts at 1, goes to 10, and increments by 1 If count = 5 then continue looping causing the program to skip the rest of the loop Create a message box that displays the output, has the title “using the continue statement,” uses an OK button, and displays an information icon.

ContinueTest.cs Program Output

5.8 Logical and Conditional Operators Operators Logical AND (&) Conditional AND (&&) Logical OR (|) Conditional OR (||) Logical exclusive OR or XOR (^) Logical NOT (!) Can be avoided if desired by using other conditional operators Used to add multiple conditions to a statement

5.8 Logical and Conditional Operators

LogicalOperators.cs 1 // Fig. 5.20: LogicalOperators.cs 2 // Demonstrating the logical operators. 3 using System; 4 5 class LogicalOperators 6 { 7 // main entry point for application 8 static void Main( string [] args ) 9 { 10 // testing the conditional AND operator (&&) 11 Console.WriteLine( "Conditional AND (&&)" + 12 "\nfalse && false: " + ( false && false ) + 13 "\nfalse && true: " + ( false && true ) + 14 "\ntrue && false: " + ( true && false ) + 15 "\ntrue && true: " + ( true && true ) ); 16 17 // testing the conditional OR operator (||) 18 Console.WriteLine( "\n\nConditional OR (||)" + 19 "\nfalse || false: " + ( false || false ) + 20 "\nfalse || true: " + ( false || true ) + 21 "\ntrue || false: " + ( true || false ) + 22 "\ntrue || true: " + ( true || true ) ); 23 24 // testing the logical AND operator (&) 25 Console.WriteLine( "\n\nLogical AND (&)" + 26 "\nfalse & false: " + ( false & false ) + 27 "\nfalse & true: " + ( false & true ) + 28 "\ntrue & false: " + ( true & false ) + 29 "\ntrue & true: " + ( true & true ) ); 30 Only true if both inputs are true Only false if both inputs are false The result is only true if both are true Outputs a truth table for the conditional AND operator (&&) Outputs a truth table for the conditional OR operator (||) Outputs a truth table for the logical AND operator (&)

LogicalOperators.cs Program Output 31 // testing the logical OR operator (|) 32 Console.WriteLine( "\n\nLogical OR (|)" + 33 "\nfalse | false: " + ( false | false ) + 34 "\nfalse | true: " + ( false | true ) + 35 "\ntrue | false: " + ( true | false ) + 36 "\ntrue | true: " + ( true | true ) ); 37 38 // testing the logical exclusive OR operator (^) 39 Console.WriteLine( "\n\nLogical exclusive OR (^)" + 40 "\nfalse ^ false: " + ( false ^ false ) + 41 "\nfalse ^ true: " + ( false ^ true ) + 42 "\ntrue ^ false: " + ( true ^ false ) + 43 "\ntrue ^ true: " + ( true ^ true ) ); 44 45 // testing the logical NOT operator (!) 46 Console.WriteLine( "\n\nLogical NOT (!)" + 47 "\n!false: " + ( ! false ) + 48 "\n!true: " + ( ! true ) ); 49 } 50 } Conditional AND (&&) false && false: False false && true: False true && false: False true && true: True Conditional OR (||) false || false: False false || true: True true || false: True true || true: True Returns the opposite as the input Returns false when the two conditionals are the same If one is true the result is true Outputs a truth table for the logical OR operator (||) Outputs a truth table for the logical exclusive OR operator (||) Outputs a truth table for the logical NOT operator (!)

LogicalOperators.cs Program Output Logical AND (&) false & false: False false & true: False true & false: False true & true: True Logical OR (|) false | false: False false | true: True true | false: True true | true: True Logical exclusive OR (^) false ^ false: False false ^ true: True true ^ false: True true ^ true: False Logical NOT (!) !false: True !true: False

5.9 Structured Programming Summary Control Structures Only one entrance Only one exit Building blocks to programming Allow nesting Makes code neater and easier to follow No overlapping structures The goto keyword

5.9 Structured Programming Summary 3 forms of control necessary Many ways to implement these controls Sequential (only 1 way) Straight forward programming Selection (3 ways) if selection (one choice) if/else selection (two choices) switch statement (multiple choices) Repetition (4 ways) while structure do/while structure for structure foreach structure (chapter 7)

5.9 Structured Programming Summary

5.9 Structured Programming Summary Fig. 5.22 C#’s single-entry/single-exit sequence, selection and repetition structures. (part 1) Sequence . .

5.9 Structured Programming Summary Fig. 5.22 C#’s single-entry/single-exit sequence, selection and repetition structures. (part 2) Selection T F if structure (single selection) else/if structure (double selection) T F switch structure (multiple selections) . . break break break break T T T F F F .

5.9 Structured Programming Summary Fig. 5.22 C#’s single-entry/single-exit sequence, selection and repetition structures. (part 3) Repetition T F while structure T F do/while structure F T for structure/ foreach structure

5.9 Structured Programming Summary Fig. 5.24 Simplest flowchart.

5.9 Structured Programming Summary . . . Rule 2 Rule 2 Rule 2 Fig. 5.25 Repeatedly applying rule 2 of Fig. 5.23 to the simplest flowchart.

5.9 Structured Programming Summary Fig. 5.26 Applying rule 3 of Fig. 5.23 to the simplest flowchart. Rule 3 Rule 3

5.9 Structured Programming Summary Fig. 5.27 Stacked, nested and overlapped building blocks. Stacked building blocks Overlapping building blocks (illegal in structured programs) Nested building blocks

5.9 Structured Programming Summary Fig. 5.28 Unstructured flowchart.

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