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Thread: How do you find the the exact index of an element that matches a search in an array?

  1. #1
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    Default How do you find the the exact index of an element that matches a search in an array?

    import java.util.*;
    public class ArrayTest {
        public static void main (String[]args) {
            Scanner input = new Scanner(System.in);
            int [] number = new int[5];
     
      System.out.println("Enter 5 numbers");
      for (int i=0; i<number.length;i++) {
            number[i] = input.nextInt();
     
        }
      }
        }
    lets say i enter 4,6,70,12,5
    I want to search for 70 (using a loop of course), and when i find it, i want to display the index it is in.in this case 2


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    Super Moderator Norm's Avatar
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    Default Re: How do you find the the exact index of an element that matches a search in an array?

    If you don't understand my answer, don't ignore it, ask a question.

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    Default Re: How do you find the the exact index of an element that matches a search in an array?

    Iterate over the array and compare each element to the target. When you get a match you have found the index. This is best achieved using a method that can return the index as soon as it is found or some other default value (-1) if it is not found.
    Improving the world one idiot at a time!

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    ojonugwa (August 23rd, 2013)

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    Default Re: How do you find the the exact index of an element that matches a search in an array?

    This is what i eventually did
    import java.util.*;
    public class ArrayTest {
        public static void main (String[]args) {
            Scanner input = new Scanner(System.in);
            int [] number = new int[5];
            int index =0;
            int numToSearchFor = 50;
      System.out.println("Enter 5 numbers");
      for (int i=0; i<number.length;i++) {
            number[i] = input.nextInt();
     
        }
    for (int i=0; i<number.length;i++) {
           ++index;
                if (number[i] == numToSearchFor) {
                    index = index-1;
                    System.out.println("Found it at index " + index);
                }
     
     
     
        }
      }
        }
    Works fine, but i was hoping there was a function in the java API that did this.

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    Default Re: How do you find the the exact index of an element that matches a search in an array?

    Are you expecting the creators of java to anticipate every single function that you can think of and write it for you? Just so when you write your own program it will be a series of method calls to API classes and you never have to write your own code every again!
    Improving the world one idiot at a time!

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    Default Re: How do you find the the exact index of an element that matches a search in an array?

    Quote Originally Posted by Junky View Post
    Are you expecting the creators of java to anticipate every single function that you can think of and write it for you? Just so when you write your own program it will be a series of method calls to API classes and you never have to write your own code every again!
    That was VERY helpful

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    Super Moderator jps's Avatar
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    Default Re: How do you find the the exact index of an element that matches a search in an array?

    Quote Originally Posted by ojonugwa View Post
    This is what i eventually did
    ...
                if (number[i] == numToSearchFor) {
                   // Then i is the correct index number, just print out i
                   // The variable "index" is unnecessary
    i was hoping there was a function in the java API that did this.
    Perhaps there is, did you look? Check out this page and see what you can find

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    Default Re: How do you find the the exact index of an element that matches a search in an array?

    import java.util.*;
     
    public class ArrayTest2 {
     
        public static void main(String[] args) {
     
    Scanner input = new Scanner(System.in);
            int[] numbers = {8, 11, 19, 84};
     
     
            int numToSearchFor;
            int i;
     
            for (i = 0; i < numbers.length; i++) {
                System.out.print(numbers[i] + ",");
            }
     
            System.out.println("\nEnter the number to search for: ");
            numToSearchFor = input.nextInt();
     
     
            for (i = 0; i < numbers.length; i++) {
              if (numbers[i] == numToSearchFor) {
                    System.out.println("\nFound "+ numToSearchFor + " at index " + i);
     
            }
        }}}
    This works perfectly, until i add an "else" statement like this
     if (numbers[i] == numToSearchFor) {
                    System.out.println("\nFound "+ numToSearchFor + " at index " + i);break;
     
            } else {
                  System.out.println("Cannot find it");break;
              }
    Then it starts to print "cannot find it"
    Why is that?

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    Super Moderator jps's Avatar
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    Default Re: How do you find the the exact index of an element that matches a search in an array?

    Quote Originally Posted by ojonugwa View Post
    Then it starts to print "cannot find it"
    Why is that?
    That may be because you search one element of the array at a time. When the first index(0) is searched, the if statement is encountered. If there is no match the else executes, the break exits the loop and no other index is considered.
    Follow the loop cycle as it would be executed, you should see how it runs the way described.

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    ojonugwa (August 23rd, 2013)

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    Default Re: How do you find the the exact index of an element that matches a search in an array?

    Finally got help from my tutor.This is one possible way to do it.
    import java.util.*;
    public class ArrayTest{
    	public static void main (String[]args){
    Scanner input = new Scanner(System.in);
        	int [] number = new int[5];
        	int numberToSearchFor;
        	int i;
        	boolean found=false;
        	for (i=0; i<number.length;i++){
        		number [i] = (int)(Math.random()*20)+1;
        		System.out.println(number[i]); 
        	}
       System.out.println("Enter number to find from available numbers: ");
        	numberToSearchFor = input.nextInt();
        	i=0;
        	while(!found&&i<number.length)
                if (number[i] == numberToSearchFor){
                     System.out.println("Found it at index " + i);
                     found=true;
                }
                else
                	i++;
        	if(!found)
                System.out.println("Cannot find it");
    	}
    }

  13. The Following User Says Thank You to ojonugwa For This Useful Post:

    jps (August 23rd, 2013)

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