Name____________________________________ APCS A (Pre-Lab Exercises – 2.3-2.5)

1. What is the difference between a variable and a constant? What reserved word is required to declare a constant?

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

b. int x = 3;

c. 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 // *******************************************************************

import java.util.Scanner; public class Average { public static void main(String[] args) { int val1, val2, val3; double average; Scanner scan = new Scanner(System.in) ;

// get three values from user System.out.println("Please enter three integers and " + "I will compute their average");

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//compute the average

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//print the average

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} } 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;

a. a + b * c _______________

b. a - b – c _______________

c. a / b _______________

d. b / a _______________

e. a - b / c _______________

f. w / y _______________

g. y / w _______________

h. a + w / b _______________

i. a % b / y _______________

j. b % a _______________

k. 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 scan = new Scanner(System.in);

System.out.print ("Enter your name, please: ") Name = scan.nextInt();

System.out.print ("What is your favorite number?); number = scan.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 scan = new Scanner(System.in);

System.out.print ("Enter two integers: "); one = scan.nextInt(); two = scan.nextInt();

System.out.print("Enter a floating point number: "); what = scan.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!"); } }