1/30/2016IT 2751 Operators Arithmetic operators: + - / * % Relational operators: == > = != Logical operators: || && !

1/30/2016IT 2752 Logical Operators (true || false) ((18 <= x) && (x <= 50)) ((18 <= x) || (x <= 50)) !(x = 5) (((x % 2) == 0) && ((x % 3) == 0)) || && ! Assume x = 10 true false

1/30/2016IT 2753 De Morgan’s law I am not a female student.  I am not female or I am not a student. I will not be in my office or in the lab.  I will not be in my office and will not be in the lab. !(A && B) is same as !A || !B !(A || B) is same as !A && !B

1/30/2016IT 2754 Branching Condition Statement list 1 T F Statement list 2 Condition Statement list T F

1/30/2016IT 2755 The Syntax of if and if-else statements if ( condition ) { statement list; } if ( condition ) { statement list1; } else { statement list2; } Indentation indicates that the statements in the statement list are at the level next to the if-else statement. Reserved words A Boolean expression (logical expression). In Java, there are two possible values: true and false. A reserved word can’t be used as an identifier

1/30/2016IT 2756 Nested if/else statement if ( condition 1 ) { if ( condition 2 ) { statement list; } else { statement list; }; statement list; } else { statement list; } Indentation indicates the level of statements.

1/30/2016IT 2757 Disney Roller Coaster Ride Ride the roller coaster Give a Mickey Measure the kid’s height, h h < 4 Next Stop No Boy or Girl? Give a Mini Yes boygirl

1/30/2016IT 2758 Disney Ride in Program – OK n = Integer.parseInt( JOptionPane.showInputDialog(“How tall is the kid?”)); // IsBoy = true or false; if (h < 4) if (IsBoy) System.out.println(“Take a Mickey”); else System.out.println(“Take a Mini.”); else System.out.println(“You can ride!!”); System.out.println(“Go to the next stop.”); but not really a good idea; put { } to improve readability

1/30/2016IT 2759 Ambiguity I saw the little girl with a binocular on the mountain top. I saw the little girl with a binocular on the mountain top. I saw the little girl with a binocular on the mountain top. I saw the little girl with a binocular on the mountain top.

1/30/2016IT Rule: else belongs to the nearest if that not yet has an else if (condition1) if (condition2) {.....; } else // not a kid {.....; } Indentation can’t help compiler

1/30/2016IT Boy Scout: Give a badge Is a kid? Welcome No Is a boy? Yes No Give a guidebook Yes No Parent?

1/30/2016IT Boy Scout: in program if (IsKid) { if (IsBoy) { System.out.println(“Take a Badge”); } else // not a kid { if (IsParent) { System.out.println(“Take a Guidebook”); } System.out.println(“Welcome, everybody!.”);

1/30/2016IT Boy Scout: wrong program if (IsKid) if (IsBoy) System.out.println(“Take a Badge”); else // not a kid if (IsParent) System.out.println(“Take a Guidebook”); System.out.println(“Welcome, everybody!.”); if (IsKid) { if (IsBoy) { System.out.println(“Take a Badge”); } else // not a boy { if (IsParent) System.out.println(“Take a Guidebook”); } System.out.println(“Welcome, everybody!.”);

1/30/2016IT Other forms of Nested if/else statements (Cascaded) I if (condition_1) statement_1; else if (condition_2) statement_2; else if (condition_3) statement_3; else if (condition_4) statement_4; else if (condition_5) statement_5; if (condition_1) statement_1; if (condition_2) statement_2; if (condition_3) statement_3; if (condition_4) statement_4; if (condition_5) statement_5; V.S.

1/30/2016IT Another form of Nested if/else statement (Cascaded) PointsGrade A 500 – 599B 400 – 499C 300 – 399D 0—299F if (points >= 600) System.out.println( “ A ” ); else if (points >= 500) System.out.println( “ B ” ); else if (points >= 400) System.out.println( “ C ” ); else if (points >= 300) System.out.println( “ D ” ); else System.out.println( “ F ” ); if (points >= 600) System.out.println( “ A ” ); if (points >= 500) System.out.println( “ B ” ); if (points >= 400) System.out.println( “ C ” ); if (points >= 300) System.out.println( “ D ” ); if (points < 300) System.out.println( “ F ” );

1/30/2016IT Other forms of Nested if/else statements (Cascaded) II if (condition_1) if (condition_2) if (condition_3) if (condition_4) statement_1; else statement_2; if ( condition_1 && condition_2 && condition_3 && condition_4 ) statement_1; else statement_2; =?=?

1/30/2016IT Switch vs. Cascaded if/else if (i == 1) statement_1; else if (i == 2) statement_2; else if (i == 3) statement_3; else if (i == 4) statement_4; else if (i == 5) statement_5; else if (i == 6) statement_6; switch (i) { case 1: statement_1; break; case 2: statement_2; break; case 3: statement_3; break; case 4: statement_4; break; case 5: statement_5; break; case 6: statement_6; break; }

1/30/2016IT Another form of Nested if/else statement (Cascaded) PointsGrade A 500 – 599B 400 – 499C D F int g = (int) (point/100); switch (g) { case 6: System.out.println( “ A ” ); break; case 5: System.out.println( “ B ” ); break; case 4: System.out.println( “ C ” ); break; case 3: System.out.println( “ D ” ); break; default: System.out.println( “ F ” ); }

1/30/2016IT Switch vs. Cascaded if/else if (i == 1) statement_1; else if (i == 2) { statement_2; statement_3; } else if (i == 3) statement_3; else if (i == 4) { statement_4; statement_5 statement_6 } else if (i == 5) { statement_5; statement_6; } else if (i == 6) statement_6; switch (i) { case 1: statement_1; break; case 2: statement_2; case 3: statement_3; break; case 4: statement_4; case 5: statement_5; case 6: statement_6; }

1/30/2016IT Definite Loops vs indefinite loops isA definite loop is a loop that number of iterations is known before the loop begins, at least the upper bound is known. I.e., repeat the loop 100 times. is notAn indefinite loop is a loop that number of iterations is not known before the loop begins, at least the upper bound is known. I.e., repeat the loop until some condition reached. Precisely speaking, there is no definite loop in Java.

1/30/2016IT while loop Condition Statement list T F while (Condition) { Statement list } for loop Statement list < n = n for (???;???;???) { Statement list } repeat n times

1/30/2016IT The general format for a for loop for (Initialization_action; Condition; Condition_update) { statement_list; } int n = Integer.parseInt( JOptionPane.showInputDialog( “ input n ” )); int sum=0; for (i=0; i<=n; i++) { sum = sum + i; } System.out.println(“This answer is ” + sum); 12 3 Summation (n-1)+ n

1/30/2016IT for (Initialization_action; Condition; Condition_update) { statement_list; } int n,f=1; n = Integer.parseInt( JOptionPane.showInputDialog( “ input n ” ) ); if (n < 0) System.out.println(“No can do!!”); else for (i=2; i<=n; i++) { f = f*i; } System.out.println(“This answer is ” + f); 12 3 Factorial of n is n  (n-1)  (n-2) ...2  1

1/30/2016IT while Condition Statement list T F while (Condition) { Statement list } while (Condition) ; { Statement list }

1/30/2016IT Compare for and while int i; for (i=2; i<=n; i++) { f *= i; } i=2; while (i<=n) { f *= i; i++; } int i; for (i=0; i<n; i++) {.... } i=0; while (i<n) {.... i++;.... }

1/30/2016IT Another form of loop: Condition Statement list T F do loop do { Statement list } while (condition); This is a common patten E.g., IT CS student has to take IT168 until he/she gets a C or better. don’t forget “;” be careful

1/30/2016IT Another example of using do-loop String answer; do { answer = JOptionPane.showInputDialog( “ y or n? ” ); } while (!answer.equals( “ y ” ) && !answer.equals( “ n ” )); Ask the user to input y (yes) or n (no), where y and n are the only two valid inputs for the program to proceed. This way, we avoid a great chance of accidentally pressing the keyboard. String answer; answer = “ x ” ; while (!answer.equals( “ y ” ) && !answer.equals( “ n ” )) { answer = JOptionPane.showInputDialog( “ y or n? ” ); }

1/30/2016IT Primality Test A prime number is a positive integer that cannot be factorized, i.e., no numbers other that 1 and itself can divide it. is 893 a prime? Is (893 % 2 == 0) ? Is (893 % 3 == 0) ? Is (893 % 4 == 0) ? Is (893 % 5 == 0) ? Is (893 % 6 == 0) ?. Is (893 % 892 == 0) ? This test is silly but can do the job! We can write a loop to test these.

1/30/2016IT Primality Test int p,r,i; // r: remainder, i: factor i=1; do { i++; r = p % i; // r is the remainder of p divided by i } while (i < p && r != 0); if (i == p) System.out.println( “ a prime number. ” ); else { System.out.println( “ not a prime number. ” ); System.out.println( “ The least factor is ” +i); } do { p = Integer.parseInt( JOptionPane.showInputDialog( “ input an number:)); } while (p <= 1);

1/30/2016IT Break a loop int i = 2; do { r = p % i; if (r == 0) break; i++; } while (i < p); The break statement in a loop will force the program to jump out of the loop immediately. int i = 2; do { r = p % i; i++; } while (i < p && r != 0);

1/30/2016IT Break a loop import javax.swing.JOptionPane;.... public static void marryAsk() { String answer; do { answer = JOptionPane.showInputDialog( "Would you marry me? (y/n)"); if (answer.equals("Y") || answer.equals("y")) answer = JOptionPane.showInputDialog( "Really? (y/n)"); } while (!answer.equals("Y") && !answer.equals("y")); JOptionPane.showMessageDialog(null, "Great!!"); } if (answer.equals("F") || answer.equals("f"))break;

1/30/2016IT break and continue The break statement in a for/while loop will force the program to jump out of the for/while loop immediately. The continue statement in a for/while loop will force the program to update the loop condition and then check the condition immediately. for (Initialization_action; Condition; Condition_update) { statement_list; }

1/30/2016IT The Loops with multiple breaking points.... while (......) {.... if (....) break;.... if (....) break;.... if (....) break;.... if (....) break;..... }.... Condition Statement list T F Spaghetti code? Why spaghetti code is bad? Well, this is not spaghetti code!

1/30/2016IT The Loops with multiple breaking points This is Spaghetti code? This is not spaghetti code! All paths come to the same point Multiple-break-loop does not cause the trouble as the spaghetti code does

35 Euclid Algorithm Public int GCD(int a, int b) { int r = a % b; while (r != 0) { a = b; b = r; r = a % b; } return (b); } 1/30/2016IT 275

My own square root function (incorrect my_sqrt) double my_sqrt(double a) { double up=a,down=0,st=a/2; if (a < 0) return -1; while (a - st*st != 0) { if (st*st > a) up = st; else down = st; st = (up+down)/2; } return st; } 1.Where can I improve the program? 2.Where is the potential problem? up down 0 a guess st real square root 1/30/201636IT 275

My own square root function (incorrect my_sqrt) double my_sqrt(double a) { double up=a,down=0,st=a/2,est; if (a < 0) return -1; est = st*st; `while (a - est > ) { if (est > a) up = st; else down = st; st = (up+down)/2; est = st*st; } return st; } Any problem? What is it? 1/30/201637IT 275

My own square root function (incorrect my_sqrt) double my_sqrt(double a) { double up=a,down=0,st=a/2,est; if (a < 0) return -1; est = st*st; while ((a - est > )||(a - est < )) { if (est > a) up = st; else down = st; st = (up+down)/2; est = st*st; } return st; } Still wrong!! What is the roblem? 1/30/201638IT 275

My own square root function (my_sqrt) double my_sqrt(double a) { double up,down,st,est; if (a < 0) return -1; if ( a >= 1) { up=a; down=0;} else { up=1; down=a;} st = (up+down)/2; est = st*st; while ((a - est > ) || (a - est < )) { if (est > a) up = st; else down = st; st = (up+down)/2; est = st*st; } return st; } 1/30/201639IT 275

1/30/2016IT Nested loops (loop in loop) int a = Integer.parseInt( JOptionPane.showInputDialog(“input a:”); int b = Integer.parseInt( JOptionPane.showInputDialog(“input b:”); for (int i = 0; i < a; i++) { for (int j=0; j<b; j++) { System.out.print(“*”); } System.out.print(“\n”); } ************* b a

1/30/2016IT Nested loops (2) int a = Integer.parseInt( JOptionPane.showInputDialog(“input a:”); int b = Integer.parseInt( JOptionPane.showInputDialog(“input b:”); for (int i = 0; i < a; i++) { for (int j=0; j<b; j++) { if (j > i) break; System.out.print(“*”); } System.out.print(“\n”); } * ** *** **** b a

1/30/2016IT Java Blocks In Java and other C-like languages: a compound statement using { and } A compound statement also serves as a block: while (i < 0) { int c = i*i*i; p += c; q += c; i -= step; } for (int i=0;i<0; i++) { int c = i*i*i; p += c; q += c; i -= step; }

1/30/2016IT Can we do this? for (int i=0; i<n; i++) {.... } int i=2; Scope of red i {}{} Scope of blue i Yes!

1/30/2016IT Can we do this? for (int i=0; i<n; i++) {.... } i=2; Scope of red i {}{} blue i is undefined No!

1/30/2016IT Can we do this? for (int i=0; i<n; i++) {.... } int i=2; {}{} Scope of blue i No!