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1 Chapter 4 - Control Structures: Part 1 2003 Prentice Hall, Inc. All rights reserved. 2 4.3 Pseudocode • Pseudocode – Informal language for developing algorithms – Not executed on computers – Helps developers “think out” algorithms 2003 Prentice Hall, Inc. All rights reserved. 3 4.4 Control Structures • Sequential execution – Program statements execute one after the other • Transfer of control – Three control statements can specify order of statements • Sequence structure • Selection structure • Repetition structure • Activity diagram – Models the workflow • Action-state symbols • Transition arrows 2003 Prentice Hall, Inc. All rights reserved. 4 add grade to total Corresponding Java statement: total = total + grade; add 1 to counter Corresponding Java statement: counter = counter + 1; Fig 4.1 Sequence structure activity diagram. 2003 Prentice Hall, Inc. All rights reserved. 5 4.4 Control Structures • Java has a sequence structure “built-in” • Java provides three selection structures – if – if…else – switch • Java provides three repetition structures – while – do…while – do • Each of these words is a Java keyword 2003 Prentice Hall, Inc. All rights reserved. 6 4.5 if Single-Selection Statement • Single-entry/single-exit control structure • Perform action only when condition is true • Action/decision programming model 2003 Prentice Hall, Inc. All rights reserved. 7 [grade >= 60] print “Passed” [grade < 60] Fig 4.3 if single-selections statement activity diagram. 2003 Prentice Hall, Inc. All rights reserved. 8 4.6 if…else Selection Statement • Perform action only when condition is true • Perform different specified action when condition is false • Conditional operator (?:) max = a > b ? a : b; • Nested if…else selection structures 2003 Prentice Hall, Inc. All rights reserved. 9 [grade < 60] print “Failed” [grade >= 60] print “Passed” Fig 4.4 if…else double-selections statement activity diagram. 2003 Prentice Hall, Inc. All rights reserved. 10 4.7 while Repetition Statement • Repeat action while condition remains true 2003 Prentice Hall, Inc. All rights reserved. 11 merge decision [product <= 1000] double product value [product > 1000] Corresponding Java statement: product = 2 * product; Fig 4.5 while repetition statement activity diagram. 2003 Prentice Hall, Inc. All rights reserved. 12 4.8 Formulating Algorithms: Case Study 1 (Counter-Controlled Repetition) • Counter – Variable that controls number of times set of statements executes • Average1.java calculates grade averages – uses counters to control repetition 2003 Prentice Hall, Inc. All rights reserved. 13 Set total to zero Set grade counter to one While grade counter is less than or equal to ten Input the next grade Add the grade into the total Add one to the grade counter Set the class average to the total divided by ten Print the class average Fig. 4.6 Pseudocode algorithm that uses countercontrolled repetition to solve the class-average problem. 2003 Prentice Hall, Inc. All rights reserved. 14 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 // Fig. 4.7: Average1.java // Class-average program with counter-controlled repetition. import javax.swing.JOptionPane; Declare variables; gradeCounter is the counter public class Average1 { public { int int int int static void main( String args[] ) total; gradeCounter; grade; average; // // // // sum of grades input by user number of grade to be entered next grade value average of grades Continue looping String gradeString; // grade typed by Outline Average1.java gradeCounter Line 21 as long as gradeCounter is less than or user equal to 10 // initialization phase total = 0; // initialize total gradeCounter = 1; // initialize loop counter // processing phase while ( gradeCounter <= 10 ) { // loop 10 times // prompt for input and read grade from user gradeString = JOptionPane.showInputDialog( "Enter integer grade: " ); // convert gradeString to int grade = Integer.parseInt( gradeString ); 2003 Prentice Hall, Inc. All rights reserved. 15 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 total = total + grade; gradeCounter = gradeCounter + 1; // add grade to total // increment counter } // end while Outline Average1.java // termination phase average = total / 10; // integer division // display average of exam grades JOptionPane.showMessageDialog( null, "Class average is " + average, "Class Average", JOptionPane.INFORMATION_MESSAGE ); System.exit( 0 ); // terminate the program } // end main } // end class Average1 2003 Prentice Hall, Inc. All rights reserved. 16 Outline Average1.java 2003 Prentice Hall, Inc. All rights reserved. 4.9 Formulating Algorithms with TopDown, Stepwise Refinement: Case Study 2 (Sentinel-Controlled Repetition) • Sentinel value – Used to indicated the end of data entry • Average2.java has indefinite repetition – User enters sentinel value (-1) to end repetition 2003 Prentice Hall, Inc. All rights reserved. 17 18 Initialize total to zero Initialize counter to zero Input the first grade (possibly the sentinel) While the user has not as yet entered the sentinel Add this grade into the running total Add one to the grade counter Input the next grade (possibly the sentinel) If the counter is not equal to zero Set the average to the total divided by the counter Print the average else Print “No grades were entered” Fig. 4.8 Class-average problem pseudocode algorithm with sentinel-controlled repetition. 2003 Prentice Hall, Inc. All rights reserved. 19 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 // Fig. 4.9: Average2.java // Class-average program with sentinel-controlled repetition. import java.text.DecimalFormat; // class to format numbers import javax.swing.JOptionPane; Outline Average2.java public class Average2 { public static void main( String args[] ) { int total; // sum of grades int gradeCounter; // number of grades entered int grade; // grade value double average; // number with decimal point for average String gradeString; // grade typed by user // initialization phase total = 0; // initialize total gradeCounter = 0; // initialize loop counter // processing phase // get first grade from user gradeString = JOptionPane.showInputDialog( "Enter Integer Grade or -1 to Quit:" ); // convert gradeString to int grade = Integer.parseInt( gradeString ); 2003 Prentice Hall, Inc. All rights reserved. 20 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 // loop until sentinel value read from user while ( grade != -1 ) { total = total + grade; //loop add until gradegradeCounter to total gradeCounter = gradeCounter + 1; // equals increment counter sentinel value (-1) // get next grade from user gradeString = JOptionPane.showInputDialog( "Enter Integer Grade or -1 to Quit:" ); // convert gradeString to int Format numbers to grade = Integer.parseInt( gradeString ); hundredth Outline Average2.java Line 31 nearest Line 45 } // end while // termination phase DecimalFormat twoDigits = new DecimalFormat( "0.00" ); // if user entered at least one grade... if ( gradeCounter != 0 ) { // calculate average of all grades entered average = (double) total / gradeCounter; // display average with two digits of precision JOptionPane.showMessageDialog( null, "Class average is " + twoDigits.format( average ), "Class Average", JOptionPane.INFORMATION_MESSAGE ); } // end if part of if...else 2003 Prentice Hall, Inc. All rights reserved. 21 60 61 62 63 64 65 66 67 68 else // if no grades entered, output appropriate message JOptionPane.showMessageDialog( null, "No grades were entered", "Class Average", JOptionPane.INFORMATION_MESSAGE ); System.exit( 0 ); // terminate application Outline Average2.java } // end main } // end class Average2 2003 Prentice Hall, Inc. All rights reserved. 4.10 Formulating Algorithms with TopDown, Stepwise Refinement: Case Study 3 (Nested Control Structures) • Nested control structures 2003 Prentice Hall, Inc. All rights reserved. 22 23 Initialize passes to zero Initialize failures to zero Initialize student to one While student counter is less than or equal to ten Input the next exam result If the student passed Add one to passes else Add one to failures Add one to student counter Print the number of passes Print the number of failures If more than eight students passed Print “Raise tuition” Fig 4.10 Pseudocode for examination-results problem. 2003 Prentice Hall, Inc. All rights reserved. 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 // Fig. 4.11: Analysis.java // Analysis of examination results. import javax.swing.JOptionPane; public class Analysis { Outline Loop until student counter is greater than 10 Analysis.java Line 19 public static void main( String args[] ) { // initializing variables in declarations int passes = 0; // number of passes int failures = 0; // number of failures int studentCounter = 1; // student counter int result; // one exam result String input; String output; // user-entered Nested value // output string Line 29 control structure // process 10 students using counter-controlled loop while ( studentCounter <= 10 ) { // prompt user for input and obtain value from user input = JOptionPane.showInputDialog( "Enter result (1 = pass, 2 = fail)" ); // convert result to int result = Integer.parseInt( input ); // if result 1, increment passes; if...else nested in while if ( result == 1 ) passes = passes + 1; 2003 Prentice Hall, Inc. All rights reserved. 25 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 else // if result not 1, increment failures failures = failures + 1; // increment studentCounter so loop eventually terminates studentCounter = studentCounter + 1; Outline Analysis.java } // end while // termination phase; prepare and display results output = "Passed: " + passes + "\nFailed: " + failures; // determine whether more than 8 students passed if ( passes > 8 ) output = output + "\nRaise Tuition"; JOptionPane.showMessageDialog( null, output, "Analysis of Examination Results", JOptionPane.INFORMATION_MESSAGE ); System.exit( 0 ); // terminate application } // end main } // end class Analysis 2003 Prentice Hall, Inc. All rights reserved. 26 4.11 Compound Assignment Operators • Assignment Operators – Abbreviate assignment expressions – Any statement of form • variable = variable operator expression; – Can be written as • variable operator= expression; – e.g., addition assignment operator += •c = c + 3 – can be written as • c += 3 2003 Prentice Hall, Inc. All rights reserved. 27 Assig nm ent Sa m p le Exp la na tion op era tor exp ression Assume: int c = 3, d = 5, e = 4, f = 6, g = 12; += c += 7 c = c + 7 -= d -= 4 d = d - 4 *= e *= 5 e = e * 5 /= f /= 3 f = f / 3 %= g %= 9 g = g % 9 Fig. 4.12 Arithm etic a ssig nm ent op era to rs. 2003 Prentice Hall, Inc. All rights reserved. Assig ns 10 to c 1 to d 20 to e 2 to f 3 to g 28 4.12 Increment and Decrement Operators • Unary increment operator (++) – Increment variable’s value by 1 • Unary decrement operator (--) – Decrement variable’s value by 1 • Preincrement / predecrement operator • Post-increment / post-decrement operator 2003 Prentice Hall, Inc. All rights reserved. 29 Op era tor Ca lled ++ preincrement ++ postincrement -- predecrement -- postdecrement Fig. 4.13 The inc rem ent 2003 Prentice Hall, Inc. All rights reserved. Sa m p le exp ression ++a Exp la na tion Increment a by 1, then use the new value of a in the expression in which a resides. a++ Use the current value of a in the expression in which a resides, then increment a by 1. --b Decrement b by 1, then use the new value of b in the expression in which b resides. b-Use the current value of b in the expression in which b resides, then decrement b by 1. a nd d ec re m ent op era tors. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 30 // Fig. 4.14: Increment.java // Preincrementing and postincrementing operators. public class Increment { Outline Line 13 postincrements c public static void main( String args[] ) { int c; // demonstrate postincrement c = 5; // System.out.println( c ); // System.out.println( c++ ); // System.out.println( c ); // System.out.println(); assign 5 to c print 5 Line 21 preincrements print 5 then postincrement print 6 Increment.java Line 13 postincrement Line 21 preincrement c // skip a line // demonstrate preincrement c = 5; // System.out.println( c ); // System.out.println( ++c ); // System.out.println( c ); // assign 5 to c print 5 preincrement then print 6 print 6 } // end main } // end class Increment 5 5 6 5 6 6 2003 Prentice Hall, Inc. All rights reserved. 31 Op era tors Assoc ia tivity Typ e ++ -right to left unary postfix ++ -- + (type) right to left unary * / % left to right multiplicative + left to right additive < <= > >= left to right relational == != left to right equality ?: right to left conditional = += -= *= /= %= right to left assignment Fig. 4.15 Prec ed enc e a nd a ssoc ia tivity of the op era tors d isc ussed so fa r. 2003 Prentice Hall, Inc. All rights reserved. 32 4.13 Primitive Types • Primitive types – “building blocks” for more complicated types • Java is strongly typed – All variables in a Java program must have a type • Java primitive types – portable across computer platforms that support Java 2003 Prentice Hall, Inc. All rights reserved. 33 Typ e boolean Size in b its char 16 byte 8 short 16 int 32 long 64 float 32 double 64 Fig. 4.16 The Ja va Va lues true or false Sta nd a rd [Note: The representation of a boolean is specific to the Java Virtual Machine on each computer platform.] '\u0000' to '\uFFFF' (ISO Unicode character set) (0 to 65535) –128 to +127 (–27 to 27 – 1) –32,768 to +32,767 (–215 to 215 – 1) –2,147,483,648 to +2,147,483,647 (–231 to 231 – 1) –9,223,372,036,854,775,808 to +9,223,372,036,854,775,807 (–263 to 263 – 1) Negative range: (IEEE 754 floating point) –3.4028234663852886E+38 to –1.40129846432481707e–45 Positive range: 1.40129846432481707e–45 to 3.4028234663852886E+38 Negative range: (IEEE 754 floating point) –1.7976931348623157E+308 to –4.94065645841246544e–324 Positive range: 4.94065645841246544e–324 to 1.7976931348623157E+308 p rim itive typ es. 2003 Prentice Hall, Inc. All rights reserved.