Lec 6 Logical Operators String comparison

Review – if statement syntax OR

3 Logical expressions is logical expression score == 100 x+y>10 ans!='y' (ans is a char) isValid (isValid is a boolean )

The 6 Comparison Operators

Sometimes we need more complicated logic – example: age is between 18 and 55 months > 3 OR miles>5000 word is not "yes" (word is String)

6 Application: How to tell if n is in the correct range...println("Enter a number from 1 to 10"); n = myInput.nextInt(); if (n>=1){ if (n<=10){ cout<<“OK, n is between 1 and 10!”; } else { cout<<“n is too big”; } } else{ cout<<“n is too small”; }

7 A better way using &&...println("Enter a number from 1 to 10"); n = myInput.nextInt(); if (n>=1 && n <=10){ cout<<“OK, n is between 1 and 10!”; } else{ cout<<“illegal value of n”; }

The 3 Logical Operators logical operator meaning example in English &&and a 10 a is less than 3 and b is greater than 10 ||or a 10 a is less than 3 or b is greater than 10 !not !(a < 3) it is not the case that a is less than 3

9 Examples 1. T/F ( 3 7) 2. T/F ! ( 2 > 3 ) 3. T/F (25 = = 25 ) || ( 2 > 3 ) 4. the expression: ( number > 10 && number < 40 ) is TRUE, when a) number is larger than 40 b) number is smaller than 10 c) number is between 10 and 40 d) Never

Oil Change

Primitives vs Objects Recall the primitives: – int x = 3; double num = 3.42; char letter = 'Y'; – boolean found = true; And objects (of Classes we've seen) – Scanner myUserInput = new Scanner(System.in); – String greeting = "hello";

Some differences between Primitives and Objects Objects have methods: – greeting.trim(); // remove blanks before/after – greeting.toUpperCase(); // convert to CAPS – myUserInput.nextInt(); // get an integer Primitives just store values: – int x = 3; double num = 3.42; char letter = 'Y'; – boolean found = true;

Comparing Strings Normally, Strings (and objects in general) should not use the comparison operators to check values: – WRONG: if ( greeting == "hello" ){.... Use.equals( ) instead – RIGHT: if (greeting.equals( "hello") {... For strings, this is even better: – if ( greeting.equalsIgnoreCase("hello"){...

True or false? String s1 = "hello", s2 = "HeLLo", s3 = " hello "; s1.equals("hello"); s2.equals("hello"); s3.equals("hello"); s2.equalsIgnoreCase("Hello"); s3.trim().equals("hello");

Lab 6 Department store Checkout.java Ask how many items to ring up – must be 1-10 – use do loop to verify correct numbers – logical operators to check for too high or too low While loop repeats for as many items – get item cost – add to total Ask if a bag is wanted, – $ 0.05 extra if only 1-3 items Add 8.25% sales tax ( total = total*1.0825)

How to avoid: total = $ EITHER: truncate (chop) to two decimal places double d = ; int i = (int)(d*100); System.out.println(i / 100.0); OR format (round) to two decimal places for output d = ; System.out.printf("%1.2f", d); System.out.println(); //need this since printf doesn't //produce a newline character

Calculating the sum or average int sum = 0; int k = 0, num; while ( k < 5) { num = scan.nextInt(); sum = sum + num; k = k + 1; }...println("sum is " + sum);...println("avg is " + sum/5.0); sumnumkk < 10 Console