Chapter 5: Booleans and Flow Control

The exercises here are taken from my book, The Java Developer's Resource.

Quiz

Is a float large enough to count the king's wheat?
Yes.
Why isn't there a ** or a // operator?
Multiplying or dividing by one doesn't change the number. The following loops are infinite.
```
	int i = 1; 
	while (i** < 2) {
	  ...
	} 
	
	while (i // > 0) {
	  ...
	}	
	
```
You may also note that // starts a one line comment (Though it wouldn't if there were a need for a real // operator).
Given that a is a boolean variable, what's the value of (a || !a)?
According to classical, Aristotelian logic and to Java (a || !a) is always true.
Here's one that stumped the author until he got some help from comp.lang.java. What's wrong with this program?

public class BytePrint {

  public void main(String[] args) {
    for (byte b = -128; b <= 127; b++) {
      System.out.println(b);
    }

  }

}

The <= should be <. Otherwise one is added to 127, which produces 128. However 128 is too large to fit in a byte so it wraps around to -128 which starts the loop over. That is, this is an infinite loop. You can also fix the problem by making b an int.

Exercises

Write the FahrToCelsius program of the last chapter using a for loop instead of a while loop.

// Print a Fahrenheit to Celsius table

class FahrToCelsius  {

  public static void main (String args[]) {
  
    double fahr, celsius;

    for (fahr = 0.0; fahr <= upper; fahr += 20.0) { 
      celsius = (5.0 / 9.0) * (fahr-32.0);
      System.out.println(fahr + " " + celsius);
    } 

  } 

}

Write the combination lock programs of Chapter 3 using for loops.

class lock {

  public static void main(String[] args)  {
    
     for (int i = 0; i <= 36; i++) {
       for ( int j = 0; j <= 36; j++) {
         for  (int k = 0; k <= 36; k++) {
           System.out.println(i + " " + j + " " + k);
         }
       }
     }
     
  }
  
}

class badlock {

  public static void main(String[] args)  {
    
     for (int i = 2; i <= 36; i += 3) {
       for ( int j = 2; j <= 36; j += 3) {
         for  (int k = 2; k <= 36; k += 3) {
           System.out.println(i + " " + j + " " + k);
         }
       }
     }
     
  }
  
}