Java: Finding an Integer in an Array

Make sure you always format your code nicely. Your intention is to return -1 if the check within the for loop is never triggered on any iteration, but you're checking if it's not triggered just on the first iteration. The program flow becomes more apparent when you add proper braces to your code:

for(int i = 0; i < theArray.length; i++) {
  if (value == theArray[i]) {
    return i; 
  }
}
return -1; // else return -1

I've also removed the extra variables - you can just return i and -1 directly.

I put your code into Eclipse, and the compiler complains that the method must return a result of type int.

What the compiler says is wrong is that if your array is passed in with 0 length, your for loop will never go into the if statements, so you need an extra return statement outside the for loop.

The other logical error that your compiler won't complain about is that you used an else statement. That means that if the array is more than length 0, after the first test you will instantly quit the function and return either 0 or -1.

eg:

public static int findElementIndex(int value, int[] theArray) {
    int index = 0;
    int n = -1;
    for (int i = 0; i < theArray.length; i++) {
        if (value == theArray[i]) {
            index = i;
            return index;
        }
    }
    return -1; // if the array was length 0, your for loop will not run.
}

Also, please use proper brackets.

Not having brackets is a very stupid idea.

You can accidentally write code like this, where you want to run the 3 do this lines inside the for loop:

for (condition)
    do this
    do this 2
    do this 3

but would actually mean

for (condition) { 
    do this 
}
do this 2
do this 3

which leaves out do this 2 and do this 3 - not what you were expecting. It's a pain to debug without brackets as well. If only you put the brackets in on the first shot.. you wouldn't even come to that problem.

You have some odd code formatting, but you also are missing a key step - you only want to return -1 if you've finished going through all the values and didn't find it! Also, you don't need to store values in a variable just to immediately return them!

Try this:

int index = 0;
for(int i =0; i < theArray.length; i++){
    if(value == theArray[i]) {
        return i; //returns where we found it if it matches
    }
}
return -1; //this line is only reached if we didn't already return