C# 0 The Complete Reference

high

. The value of 

high

 is then incremented because the indexes specified 

are inclusive. Next, a check is made to ensure that the upper index is greater than the lower 

index. If not, an error is reported and a one-element array is created. Next, storage for the 

array is allocated and assigned to 

a

. Then the 

Length

 property is set equal to the number of 

elements in the array. Finally, 

lowerBound

 and 

upperBound

 are set.

Next,

RangeArray

 implements its indexer, as shown here:

// This is the indexer for RangeArray.

public int this[int index] {

  // This is the get accessor.

  get {

    if(ok(index)) {

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      Error = false;

      return a[index - lowerBound];

    } else {

      Error = true;

      return 0;

    }

  }

  // This is the set accessor.

  set {

    if(ok(index)) {

      a[index - lowerBound] = value;

      Error = false;

    }

    else Error = true;

  }

}

This indexer is similar to the one used by 

FailSoftArray

, with one important exception. 

Notice the expression that indexes 

a

. It is

index - lowerBound

This expression transforms the index passed in 

index

 into a zero-based index suitable for 

use on 

a

. This expression works whether 

lowerBound

 is positive, negative, or zero.

The

ok( )

 method is shown here:

// Return true if index is within bounds.

private bool ok(int index) {

  if(index >= lowerBound & index <= upperBound) return true;

  return false;

}

It is similar to the one used by 

FailSoftArray

 except that the range is checked by testing it 

against the values in