Looping an array

Question

  void searchForPopulationChange()
  {
     String goAgain;
     int input;
     int searchCount = 0;
     boolean found = false;

     while(found == false){
        System.out.println ("Enter the Number for Population Change to be found: ");
        input = scan.nextInt();



        for (searchCount = 0; searchCount < populationChange.length; searchCount++)
        {
           if (populationChange[searchCount] == input)
           {
              found = true;
              System.out.print(""+countyNames[searchCount]+" County / City with a population of "+populationChange[searchCount]+" individuals\n");
           } 

        }


     }
  }

}

hello! I am working on a method that will take an users input, lets say (5000) and search a data file with those corresponding numbers. and return the corresponding number, and county that it corresponds with.

However, I am able to get this code to run to return the correct value, but i am unable to get it to run when i enter an "incorrect" value.

Any pointers? Thank you!

What do you mean by an "incorrect value"? Out of range number? Decimal? Not even a valid number? — nanofarad
– nanofarad, Commented Jul 19, 2013 at 1:01
What do you expect to happen? What is happening? You might want to consider posting more of your code so we can run it ourselves. — Jeffrey
– Jeffrey, Commented Jul 19, 2013 at 1:05
It is a huge code, I dont think i can post it all on here. Basically I want the program to search a data file ( an array) There is a county with populations next to it. I want to search this data file by entering a population number. The program will then return the corresponding "county" that has that population. — user2517185
– user2517185, Commented Jul 19, 2013 at 1:08
What i want to happen when i enter an invalid number, is for the code to loop at and tell the user "Error" and to "re enter" a correct population # — user2517185
– user2517185, Commented Jul 19, 2013 at 1:08
Did you try testing found and producing your error message if that was false? (Also, of course, you should break when the answer is found, to short-circuit the inner loop, or incorporate found in your for test.) — Hot Licks
– Hot Licks, Commented Jul 19, 2013 at 1:44

Mark M · Accepted Answer · 2013-07-19 01:31:19Z

2

It's a bit unclear, but I assume you want something to handle if the input is incorrect (not an integer)? Use hasNextInt so you will only capture integers.

Scanner scanner = new Scanner(System.in);
while (!scanner.hasNextInt()) {
    scanner.nextLine();
}
int num = scanner.nextInt();

This will keep looping the input until it is a valid integer. You can include a message in the loop reminding the user to input a correct number.

If you want something to display if your number has no match inside of the array, simply add code after your for block, if found == false. For example:

for (searchCount = 0; searchCount < populationChange.length; searchCount++)
    {
       if (populationChange[searchCount] == input)
       {
          found = true;
          System.out.print(""+countyNames[searchCount]+" County / City with a population of "+populationChange[searchCount]+" individuals\n");
       } 

    }
if (found == false) {
     System.out.println("Error, No records found!");
}

Since found is still false, your while loop kicks in and prints your line requesting for input again.

EDIT: Since you seem to have problem adding these two concepts to your code, here's the whole function:

void searchForPopulationChange() {
 String goAgain;
 int input;
 int searchCount = 0;
 boolean found = false;

 while(found == false){
    System.out.println ("Enter the Number for Population Change to be found: ");
    Scanner scanner = new Scanner(System.in);
    while (!scanner.hasNextInt()) {
      scanner.nextLine();
      }
    input = scanner.nextInt();

    for (searchCount = 0; searchCount < populationChange.length; searchCount++)
    {
       if (populationChange[searchCount] == input)
       {
          found = true;
          System.out.print(""+countyNames[searchCount]+" County / City with a population of "+populationChange[searchCount]+" individuals\n");
       } 

    }

    if (found == false) {
       System.out.println("Error, No records found!");
    }
  }
}

edited Jul 19, 2013 at 1:31

answered Jul 19, 2013 at 1:05

Mark M

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11 Comments

user2517185 Over a year ago

Where would i be placing this?

user2517185 Over a year ago

The input is inccorect if it is not a valid matchig number inside of the array.

Mark M Over a year ago

After System.out.println ("Enter the Number for Population Change to be found: ");. Just change your input input = scan.nextInt(); to utilize the scanner.

user2517185 Over a year ago

Im sorry, i am still not following this? so i am changing my while (found == false) into while (!scanner.hasNextInt()){ scanner.nextLine(); ?

Azad Over a year ago

+1 for the technic, @user2517185: after the for-loop check if(!found) (means found still false), if it was false, it means that no match was found.

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