Determining number of teenagers living in a street

Question

I'm creating a java program to determine how many people are in a street, and how many of those people are teenagers. The information is gathered from an input file which is featured below.
INPUT FILE*
12 20 13 19 34 80 0 14 75 17 50 1 11 11 30 90 15 16 70 50 -2
CODE*
/* Session7A07.java */
/* Determines number of teenagers living in a street */
import java.util.*;
import java.io.*;
public class Session7A07
  public static void main (String[] args) throws FileNotFoundException
   /* variable declarations */
   int    age,
          people_count,
          teenage_count ;
   File age_file = new File("Session7A07.txt");
   Scanner age_data = new Scanner(age_file);
   age = age_data.nextInt();
   while (age >= 0)
      ++ people_count ;
      if (age >= 13 && age <= 19)
              ++ teenage_count;     
      age = age_data.nextInt();
   System.out.printf ("Teenage Count = %d%n", teenage_count) ;
   System.out.printf ("People Count = %d%n", people_count) ;
ERRORS_
M:\>javac Session7A07.java
Session7A07.java:23: variable people_count might not have been initialized
      ++ people_count ;
         ^
Session7A07.java:25: variable teenage_count might not have been initialized
                 ++ teenage_count;
                    ^
Session7A07.java:29: variable teenage_count might not have been initialized
   System.out.printf ("Teenage Count = %d%n", teenage_count) ;
                                              ^
Session7A07.java:30: variable people_count might not have been initialized
   System.out.printf ("People Count = %d%n", people_count) ;
                                             ^
4 errorsCurrently have 4 errors and would greatly appreciate the help.
Thanks in advance.

Answer 1

redfalconf35 wrote:
int age,
people_count,
teenage_count ;the compiler doesn't like that you declared your variables but didn't initialize them to a valueTo expand on that: Member variables (those declared in the class, but outside of a method) are initialized with a default value if you don't explicitly initialize them. Variables declared in a method aren't given a default value, so if you use them without first setting their value, the compiler complains. Your while loop's body isn't guaranteed to be entered, so there's no guarantee that your variables will be set before use.