Method that takes an int array and a value and returns the index of that value in the array

Question

I've spent like an hour trying to figure this one out and I couldn't. This is an exercise for a Java elective course I am taking and I could use some help.

Write a method linearSearch() that takes an array of integers, and an integer value. It should then return the index of the value inside the array (by using a for loop to traverse the elements one by one in order). If the value is not found, -1 should be returned. If more than one value is found, the first occurrence should be returned. Write a program to test your method.

So this is what I tried doing.

public class Exercise6 {
    public static void main(String [] args) {
        int[] a = {3, 6, 70, 3, 7, 9};
        linearSearch(a, 3);
        
    }

    public static void linearSearch(int[] a, int n){  
        int index;      

        for (int i = 0; i < a.length; i++){
            if (a[i] == n){
                index = i;
                break;
            }
            else {
                index = -1;
            }
        }
        System.out.print(index);
    }
}

But this is obviously wrong. Could you please point me in the right direction? I don't necessarily want you to give me the answer, just give me an idea about the steps.

you don't need that variable index. Once you found your match, just return the index. "This is obviously wrong." Why is it wrong? What's wrong with it? — Stultuske, Mar 23 '22 at 14:15
Why do you think your code is wrong? Because it prints `0` (which is the correct solution)? — maloomeister, Mar 23 '22 at 14:17
One thing that is wrong, is that your method doesn't return anything. It should return the index, not just print something. — Stultuske, Mar 23 '22 at 14:17
Your method does not "return" anything it currently just prints. If you need a method that returns then reading [Differences between System.out.println() and return in Java](https://stackoverflow.com/questions/25456472/differences-between-system-out-println-and-return-in-java) might be a good idea. — OH GOD SPIDERS, Mar 23 '22 at 14:18

score 0 · Answer 1 · answered Mar 23 '22 at 14:38

The problem is that you didn't initialize the variable (index):

int index = -1;

but you should think at another way as follows:

1 - read what you want to do

2- You need to make a function that return the index of a specific value of array

3- Define the return type of the function ==> you need to return the index then the function return type is int

4- Define the parameters ==> you have 2 parameters : array and the value

5- You should return the index of value or -1 if it doesn't exist then you will initialize the index = -1

6- Code will be as follows:

public class Exercise6
{
    public static int linearSearch(int[] a, int n){  
        int index = -1;      

        for (int i = 0; i < a.length; i++){
            if (a[i] == n){
                index = i;
                break;
            }
        }
        return index;
    }

    public static void main(String[] args) {
        int[] a = {3, 6, 70, 3, 7, 9};
        System.out.println(linearSearch(a, 7));
    }
}

Think before Coding

All the best

WJS · Accepted Answer · 2022-03-23T16:19:21.710

There are several problems.

you want to return a value so you need to show that in the method by having a return type of int and not void.
you don't need an index variable, you already have one in your for loop (i) so use that.
As you iterate over the loop, as soon as you find the value, just do a return i; to return the index. You do not need any break statements in your method.
you don't need to keep assigning -1 to index so get rid of the else clause (remember you don't even need index).
if you finish the loop the value must not be there so just return -1;.
and lastly since you are returning a value, you need to assign it when you call the method. So do int ret = linearSearch(a, 3);. Then print the value.

score -1 · Answer 3 · answered Mar 23 '22 at 14:23

-1

This will through compilation error as int index; is not initialized. Once initialized, else part would become redundant. Rest would work and deliver you the expected output.

answered Mar 23 '22 at 14:23

Shruti Chakraborty

11
3

Method that takes an int array and a value and returns the index of that value in the array

3 Answers3