[recursion]- can someone look at this program?
I need to add 10 integers in an array using recursion, i am getting the error:
C:\MCS142\Recursion.java:5: '.class' expected
this.addArray(array[], first, last);
publicclass Recursion
{
publicstaticvoid main(String[] args)
{
this.addArray(array[], first, last);
}
int[] array ={1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
int first = 0;
int last = 9;
int sum = 0;
publicvoid addArray(int array[],int first,int last)
{
if (first < last)
sum = sum + array[first];
addArray(array, first + 1, last);
System.out.println(sum);
}
}
[1355 byte] By [
LuckY07a] at [2007-11-26 20:00:27]
> I need to add 10 integers in an array using
> recursion, i am getting the error:
>
> C:\MCS142\Recursion.java:5: '.class' expected
> this.addArray(array[], first, last);
You can't call the addArray(..) method on a method, which is what you're telling it to do with the 'this' keyword; this error is telling you that you must call the addArray(...) method on an object, such as a class. Try removing 'this'.
You error isn't related to recursion, it's how to pass an array to a method: don't include [ ]:addArray(array[], first, last); //noaddArray(array, first, last); //yes
isnt that what recursion is, calling a method inside another method? How would I fix this program? tks.
see reply #2, you haven't declared any int[] array.
I changed the code to the following, but am now getting this error:
C:\MCS142\Recursion.java:6: non-static variable array cannot be referenced from a static context
a.addArray(array, first, last);
^
C:\MCS142\Recursion.java:6: non-static variable first cannot be referenced from a static context
a.addArray(array, first, last);
^
C:\MCS142\Recursion.java:6: non-static variable last cannot be referenced from a static context
a.addArray(array, first, last);
^
3 errors
public class Recursion
{
public static void main(String[] args)
{
Recursion a = new Recursion();
a.addArray(array, first, last);
}
int[] array = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
int first = 0;
int last = 9;
int sum = 0;
public void addArray(int array[], int first, int last)
{
if (first < last)
sum = sum + array[first];
addArray(array, first + 1, last);
System.out.println(sum);
}
}
> isnt that what recursion is, calling a method inside> another method? How would I fix this program? tks.You could start by following the suggestions in Reply 1 and Reply 2.
I give up:
public class Recursion {
public static void main(String[] args) {
int[] array = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
int sum = addArray(array);
System.out.println("answer = " + sum);
}
public static int addArray(int[] array) {
return add(array, 0, array.length);
}
public static int add(int[] array, int lo, int hi) {
if (lo < hi)
return array[lo] + add(array, lo+1, hi);
else
return 0;
}
}
> isnt that what recursion is, calling a method inside
> another method? How would I fix this program? tks.
You can call a method inside a method, but you cannot call a method on another method. With the 'this' keyword, you're basically saying:
main.addArray(...)
Your main method cannot have an array added to it (or a method called on it).
thank you very much for that code. I was wondering if you could delete the method 'addArray'? and do the adding in 'add' and call add from the driver?
Feel free to edit the code. I think that having a top-level method thatjust takes an array is a nice touch, though.
I tried to simplify the code, and I got the following message, even though I have a return statement:
C:\MCS142\Recursion.java:14: missing return statement
}
public class Recursion
{
public static void main(String[] args)
{
int[] array = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
int sum = addArray(array, 0, array.length);
System.out.println(sum);
}
public static int addArray(int array[], int first, int last)
{
if (first < last)
return array[first] + addArray(array, first+1, last);
}
}
What value does addArray return if "first < last" is false?
I figured it out. I guess if you have a RETURN statement in an IF loop, you need an ELSE statement with a return. Thanks for the help, here is my completed code:
public class Recursion
{
public static void main(String[] args)
{
int[] array = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
int sum = addArray(array, 0, array.length);
System.out.println("answer = " + sum);
}
public static int addArray(int array[], int first, int last)
{
if (first < last)
return array[first] + addArray(array, first+1, last);
else
return 0;
}
}
So what you did is get rid of my lovely top-level method. *Sob*
I am trying to go backwards, and am getting an out of bounds exception.
Here is the code:
public class Recursion2
{
public static void main(String[] args)
{
int[] array = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
int sum = addArray(array, 0, array.length);
System.out.println("answer = " + sum);
}
public static int addArray(int array[], int first, int last)
{
if (first <= last)
return array[last] + addArray(array, first, last - 1);
else
return 0;
}
}
Recall that addArray(int array[], int first, int last) adds up the values of array[j], where first <= j < last.
im kinda confused. Where am I going wrong in my code? tks.
What's going wrong is that you are not grasping the significance of first and last.
Again, addArray(int array[], int first, int last) adds up the values of array[j], where first <= j < last.
As an example, suppose I define:
int[] v = {7,8,9};
What is the value of v.length? What is the offset of value 9 in this array?
v.length would be 3. I fixed the code by removing array.length and replacing it with array.length - 1. I guess I just am having a tough time seeing how it runs, I will look at it closer.. tks.
Note: There is no such thing as an if loop.
> Note: There is no such thing as an if loop.I missed that.
I am trying to divide the array in half, and then add the sum of integers recursively.. It looks like it should work, however I am getting a .class error:
C:\MCS142\Recursion3.java:24: '.class' expected
int sum = array[first] + addArray(array, first + 1, mid);
^
C:\MCS142\Recursion3.java:24: not a statement
int sum = array[first] + addArray(array, first + 1, mid);
^
C:\MCS142\Recursion3.java:30: '.class' expected
int sum2 = array[mid2] + addArray(array, mid2+1, last);
^
C:\MCS142\Recursion3.java:30: not a statement
int sum2 = array[mid2] + addArray(array, mid2+1, last);
/**
Program that demonstrates recursion using an array.
@task = to add up all integers in the array using 3 types of recursion.
*/
public class Recursion3
{
public static void main(String[] args)
{
int[] array = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
int total = addArray(array, 0, array.length);
System.out.println("answer = " + total);
}
public static int addArray(int array[], int first, int last)
{
int mid = (first + last)/2;
addArray(array, first, mid);
if (first < mid)
int sum = array[first] + addArray(array, first + 1, mid);
addArray(array, mid + 1, last);
int mid2 = mid + 1;
if (mid2 < last)
int sum2 = array[mid2] + addArray(array, mid2+1, last);
return sum + sum2;
}
}
Message was edited by:
LuckY07
