How to Swap Value in Eiffel Programming Language?

Question

I am defining like this in eiffel to swap the value. We cannot use the way we define in c++.

 swap(x,y):INTEGER
         do
            x;y := y;x
       end

How to define functions in Eiffel? I want to define heap sort but it is showing some error can someone help me clear my doubt about function.

 heapsort(array,N):INTEGER  -- heap_sort
            do
                heap_size : INTEGER
                heap_size := N

                build(array,N)

                from i := N until i >=2 loop

                    swap(array(1), array(i))
                    heap_size := heap_size-1
                    heapify(array,1,heap_size-1)

                end
            end

score 1 · Answer 1 · answered Nov 17 '19 at 14:31

All variables in Eiffel are passed by value, so there is no way to pass two variables or expressions and swap their values. As a result, the swap should look like

swap (i, j: INTEGER; data: ARRAY [...]) -- Here and below `...` stands for the type of elements.
        -- Swap items of `data` at indexes `i` and `j`.
    require
        valid_i: data.valid_index (i)
        valid_j: data.valid_index (j)
    local
        value: ...
    do
        value := data [i]
        data [i] := data [j]
        data [j] := value
    ensure
        new_at_i: data [i] = old data [j]
        new_at_j: data [j] = old data [i]
    end

Then, the call to this procedure in your example would look like

swap (1, i, array)

Side notes.

It's unclear why the feature heap_sort returns an integer. Also, it should specify types of arguments like
```
heap_sort (array: ARRAY [...]; N: INTEGER)
```
Do you really need N? It's possible to retrieve lower and upper bounds of the array with array.lower and array.upper.
Code and declarations in Eiffel are split, so you would write
```
local
    heap_side: INTEGER
do
    heap_size := N
```
The expression after until specifies the condition when loop should terminate. With the current condition i >= 2 the loop would never execute because i >= 2 is true right from the beginning.

How to Swap Value in Eiffel Programming Language?

1 Answers1