1. Lec 6 Logical Operators String comparison

2. Review – if statement syntaxOR

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

4. The 6 Comparison Operators

5. 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. Flowchart of previous slide

8. 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”;

9. The 3 Logical Operators logical operator meaning && and || or ! not
example
in English
&&
and
a < 3 && b > 10
a is less than 3 and b is greater than 10 || or
a < 3 || b > 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

10. Examples 1. T/F ( 3 < 2 ) && (5 > 7) 2. T/F ! ( 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

11. Oil Change

12. In groups, flowchart previous slide

13. 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";

14. 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;

15. 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"){ ...

16. 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");

17. 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)

18. 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\n", d); // means print d with two digits after decimal // %1.2f is format, \n means go to new line after

19. Calculating the sum or average
num k
k < 10
Console
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);