Thread: Using i-1 in programs

Here is the question: Given an array of ints, return the number of times that two 6's are next to each other in the array. Also count instances where the second "6" is actually a 7.
Here is the code:
public int array667(int[] nums) {
int len = nums.length;
int count = 0;
for (int i=0;i<len-1;i++){
if ((nums[i]==6) && (nums[i+1]==6||nums[i+1]==7)){
count++;
}
}
return count;


}
I don't understand why it has to be initialized at i-1 in order to work. Please explain
Also are there any other scenarios in which i-1 would be needed maybe even not for just initializing i.

I don't see it as well but if you meant the "len-1" in your for loop, then it could easily be explained. First of all, you aren't initializing "len-1" but rather setting up a certain condition for the for loop. The reason you need the "-1" is because "len" is the length of the entire array. It seems that you understand that arrays always start at index [0], since the .length() function returns the size of the entire array, you need to compensate with a "-1" in the condition, such that the array doesn't go out of bounds. Say you create an array with the size 10, an array will be created with the array index[0] to array[9]. The length() function would return 10 but you would have to use "-1" in your for loop because array[10] doesn't exist. Sorry if this is a bit confusing.

I'd recommend reading: Arrays (The Java™ Tutorials > Learning the Java Language > Language Basics)

@Actinistia myArray.length is more of a variable than a function and does not include () in its use.

@JoshKesner A sample program that shows what has been explained:

/** FILE: forumsamples.Arrays_IndexVsSize.java*/
package forumsamples;
 
 
 
 
/**
 * @author jps<br>
 *         This class shows the creation of an array of a given number of elements by doing a sysout each step of the way.<br>
 *         You can expect to see the difference between the index number of the last element vs the number of elements in the array.
 */
public class Arrays_IndexVsSize {
 
 
 
	/**
	 * @param args
	 *           Not used
	 */
	public static void main(String[] args) {
		//sysoutArrayConstruction(0);//Try to predict the output for this call before uncommenting it
		sysoutArrayConstruction(1);
		sysoutArrayConstruction(5);
		sysoutArrayConstruction(10);
		sysoutArrayConstruction(14);
	}
 
 
 
	/**
	 * Display the step by step creation and initialization of an array with numberOfElements elements
	 * 
	 * @param numberOfElements
	 *           The number of elements for the array to be created with
	 */
	public static void sysoutArrayConstruction(int numberOfElements) {
		int[] testArray = new int[numberOfElements];
		System.out.println("numberOfElements = " + numberOfElements + " and testArray.length = " + testArray.length);
		for(int i = 0; i < testArray.length; i++) {
			testArray[i] = i;
			System.out.print("index# " + i + " has value: " + i + " || ");
		}
		System.out.println();
	}
 
}

for (int i=0; i<len-1; i++){

Where len is anyArray.length is not what it seems. This loop will omit the last index because of the -1 because of the way the conditional is written:
i < len-1
When i = len, the loop will not run. Add the -1 in my sample above and see what happens. So the line in my sample above will become:
for(int i = 0; i < testArray.length-1; i++) {
Run it again. Compare the results.
Now change the line to:
for(int i = 0; i <= testArray.length-1; i++) {
Using <=, and -1 you get the same results as using < and no -1

@jps You're absolutely correct. I apologize for the misleading information. The message I wanted to get through was horribly worded and I probably should of just posted the link. Again, sorry for the false info. The last thing I wanted to do was confuse the OP. Thank you for the correction and for the sample program.