CS7 Notes 
from Feb. 2, 2004 

So Far Our programs have been sequential only 
  - Limiting and not interesting 
  - We want our programs to make decisions 
  - concept is based on Booleans (true, false) 

e.g. IQ 

  System.out.print(“Enter for your IQ:”); 
  IQ = Console.in.readInt(); 

  If ( IQ >= 140) 
    System.out.println(“You are smart!”); 
  System.out.println(“Thanks for playing!”); 


- Without braces, the if statement will include only one line
  of code (the "smart" line).
- Thus, the second println statement ("Thanks..") will always
  execute, no matter what (it comes after the if).

- If you add braces, you can have any number of lines in the 
  body of the if:

  If ( IQ >= 140) {
    System.out.println("You are smart!");
    System.out.println("and sexy.");
  }
  System.out.println("Thanks for playing!");


Building boolean expressions:

- Relational Operators: <, >, = =, != 

- Logical Operators:  &&(and), || (or), !(Not) 

To get a true result:
- and (&&), both parts must be true
- or (||), either part must be true
- not (!), expression must be false
- Anything else, you get false as the result.

e.g. Is the age between 18 and 25 inclusive? 

    if ((age > = 18) && (age < = 25)) 
       System.out.println(“You pay higher insurance”); 

e.g. Are you an even numbered age? 

    if (age % 2 == 0) 
       System.out.println("an even age!");


Variatons on condition:

  !(age % 2 == 0) ==> checks for oddness (negation of even)

  (age % 2 == 1)  ==> checks for oddness (looks for a 1 remainder)

  (age % 2 != 0)  ==> again checks for oddness (looks for nonzero rem.)


Note:  
  - In general, to check divisibility by n, just % by n and look
    for a zero remainder.

    if (a % n == 0)
       System.out.println(a + " is evenly divisible by " + n);


e.g. Is your age less than 6 or greater than 60? 

  If ( age < = 6 || age >= 60)
     System.out.println("Passenger needs assistance.");