Using an Accumulator

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Revision as of 18:33, 20 June 2009 by Andr3w (Talk | contribs) (Using an accumulator to find the maximum)

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When using an accumulating variable there are three stages:

Initialise
We declare our accumulator and set it to an initial values.
Update
Inside the loop we update the accumulator - we take into account the current data item.
Output/use
After the loop our accumulator contains the required value. We use it or output it.

Using an accumulator to add

Print the total of all of the numbers

  • We initialise to 0.
  • We add to the accumulator.
  • The value printed is the sum 0+2+7+1+1.


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Using an accumulator to count

Print the number of items in the list.

  • We initialise to 0.
  • We increment the accumulator.
  • The value printed is the count: 0+1+1+1+1.


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Using an accumulator to count on a condition

Count the number of 1s in the list

  • We initialise to 0.
  • We increment the accumulator only if the current value equals 1.


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Using an accumulator to multiply

Print the product of the numbers.

  • We initialise to 1. (If you initialise to 0 then the result will always be 0.)
  • We multiply the accumulator.
  • The value printed is the product: 1*2*7*1*1


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Using an accumulator to find the maximum

Print the largest number in the list.

  • We initialise to 0.
  • We take the max.
  • The value printed is the largest:

At each stage the accumulator stays the same or gets bigger (set to the current value).

max(max(max(max(0,2),7),1),1)


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Using an accumulator to concatenate

Concatenate all items in the list

Notice that we are using a list of strings this time.

  • We initialise to the empty string "".
  • We concatenate the next value (stick at the end).

WARNING - Using an accumulator like this can use a great deal of memory. You will find using a StringBuilder is more efficient.

StringBuilder acc = new StringBuilder();
for (String s:new String[]{"one","two"})
{
  acc.append(s);
}
System.out.println(acc);


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Using two accumulators to find the mean

Print the mean of all items in the list.

  • We initialise both sum and count to 0.
  • We add to the sum and increment the count.
  • We divide the sum by the count to get the average.


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