Answer:
- What is an advantage of this form of input file?
- You don't have to count up how many integers are to be averaged.
- What is a disadvantage of this form of input file?
- The integers must all be positive or zero.
It often happens that a programmer will pick a sentinel value that will "never occur in the data." Of course, years later the program is used in a new situation where that special value does occur in the data and problems arise.
Some of the "Year 2000" problems were this type of bug. The program controlling one model of VCR used the value 99 as a sentinel. These VCRs stopped working in the year 1999.
Here is part A of the program that will work with this type of input data file. Of course, there are some blanks for you to fill.
import java.io.*;
import java.util.Scanner;
class TestGroupsSentinel
{
public static void main ( String[] args ) throws IOException
{
int value; // the value of the current integer
// Prompt for and open the input file
Scanner user = new Scanner( System.in );
System.out.print("File name? ");
String fileName = user.next().trim();
Scanner scan = new Scanner( new File(fileName) );
// Group "A"
int sumA = ______; // initialize the sum of scores for group "A"
int countA = ______; // initialize the group A count
while ( (value = scan.nextInt()) != -1 )
{
sumA = ______ ; // add to the sum
countA = countA + 1; // increment the count
}
if ( countA > ______ )
System.out.println( "Group A average: " + ((double) sumA)/countA );
else
System.out.println( "Group A has no students" );
Of course, you are eager to fill in those blanks.