Prelab Exercises
Sections 2.3 - 2.4

1. What is the difference between a variable and a constant?

   
   
   

2. Explain what each of the lines below does. Be sure to indicate how each is different from the others.
   1. int x;

      
      

   2. int x = 3;

      
      

   3. x = 3;

   
   

3. The following program reads three integers and prints the average. Fill in the blanks so that it will work correctly.

   
   // *******************************************************************
   //   Average.java
   //
   //   Read three integers from the user and print their average
   // *******************************************************************
   
   
   public class Average
   {
     public static void main(String[] args)
     {
       int val1, val2, val3;
       double average;
   
       // get three values from user
       System.out.println("Please enter three integers and " +
                          "I will compute their average");
   
       ____________________________________
   
       ____________________________________
   
       ____________________________________
   
       //compute the average
   
       ____________________________________
   
       //print the average
   
       ____________________________________
   
     }
   
   }
   

   
   
   
   
4. Given the declarations below, find the result of each expression.

   int a = 3, b = 10, c = 7;
   double w = 12.9, y = 3.2;

   1. a + b * c

   2. a - b - c

   3. a / b

   4. b / a

   5. a - b / c

   6. w / y

   7. y / w

   8. a + w / b

   9. a % b / y

   10. b % a

   11. w % y

5. Carefully study the following program and find and correct all of the syntax errors.

   // File:     Errors.java
   // Purpose:  A program with lots of syntax errors
   //           Correct all of the errors (STUDY the program carefully!!)
   
   #import java.util.Scanner;
   
   public class errors
   {
      public static void main (String[] args)
      {
          String Name;  / Name of the user 
          int number;
          int numSq;
   	   Scanner myInput = new Scanner(System.in);
   
          System.out.print ("Enter your name, please: ")
          Name = myInput.nextInt();
   
          System.out.print ("What is your favorite number?);
          number = myInput.nextInt();
   
          numSq = number * number;
   
          System.out.println (Name  ", the square of your number is "
                     numSquared);
   
   }
   
   

6. Trace the execution of the following program assuming the input stream contains the numbers 10, 3, and 14.3. Use a table that shows the value of each variable at each step. Also show the output (exactly as it would be printed).

   
       // FILE:  Trace.java
       // PURPOSE:  An exercise in tracing a program and understanding
       //           assignment statements and expressions.
   
       import java.util.Scanner;
       
       public class Trace
       {
          public static void main (String[] args)
          {
             int one, two, three;
             double what;
   		  Scanner myInput = new Scanner(System.in);
   
             System.out.print ("Enter two integers: ");
             one = myInput.nextInt();
             two = myInput.nextInt();
         
             System.out.print("Enter a floating point number: ");
             what = myInput.nextDouble();
   
             three = 4 * one + 5 * two;
             two = 2 * one;
             System.out.println ("one " + two + ":" + three);
   
             one = 46 / 5 * 2 + 19 % 4;
             three = one + two;
             what = (what + 2.5) / 2;
             System.out.println (what + " is what!");
          }
       }