Databases
StackOverflow2013
Postsdbo
POHow to find the Nth element of a list, and print said element out?
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POHow to find the Nth element of a list, and print said element out?
    primarykey
    data
    text
    <p>so i have a homework question that asks me to find the third element of a list, as well as the last element of a list and print them out (2 separate programs).</p> <p>I Thought my Code would work to find the third element, by keeping track of a index, but i recieve a error when i try to run the code:</p> <pre><code>findthird([], Result). findthird(List, Result) :- secondFunc(List, 0, Result). secondFunc([Head|Tail], Count, Result) :- Count &lt; 3, Count is Count+1, secondFunc(Tail, Count, Result). secondFunc([Head|Tail], Count, [Head|Result]). </code></pre> <p>Have any ideas for this?</p> <p>The output i receieve now Is :</p> <pre><code>| ?- findthird([2,3,4], Result). Result = [2|_] yes </code></pre> <p>I am still having a tough time wrapping my head around Prolog, i just cant seem to understand it.</p> <p>Any help is appreciated as always,</p> <p>Thank.</p> <p>Updated with new attempt code***</p> <p>Updated ** This is the code that solved my problem:</p> <pre><code>findthird([], Result). findthird(List, Result) :- secondFunc(List, 0, Result). secondFunc([], Count, []). secondFunc([Head|Tail], Count, Result) :- Count1 is Count+1, Count1 &lt; 3, secondFunc(Tail, Count1, Result). secondFunc([Head|Tail], Count, Head). </code></pre> <p>Input:</p> <pre><code>| ?- findthird([3,4,5], Result). </code></pre> <p>Output:</p> <pre><code>Result = 5 ? yes </code></pre> <p>Input:</p> <pre><code>| ?- findthird([3,4,5,6,7], Result). </code></pre> <p>Output:</p> <pre><code>Result = 5 ? yes </code></pre>
    singulars
    1. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. PTQuestion
    1. USjordan.peoples
    1. USjordan.peoples
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    1. VO
      singulars
      1. POHow to find the Nth element of a list, and print said element out?
      1. This table or related slice is empty.
      1. VTDownMod
    2. VO
      singulars
      1. POHow to find the Nth element of a list, and print said element out?
      1. This table or related slice is empty.
      1. VTUpMod
    1. COGenerally, if you get an error message when trying to run? compile? a program, it is best if you share the error message with others. :)
      singulars
      1. POHow to find the Nth element of a list, and print said element out?
      1. USsarnold
    2. COsorry, will do.
      singulars
      1. POHow to find the Nth element of a list, and print said element out?
      1. USjordan.peoples
    3. COalright, the error is up: | ?- findthirdmember([1,2,3,4,5], Result). uncaught exception: error(type_error(evaluable,length/1),(is)/2)
      singulars
      1. POHow to find the Nth element of a list, and print said element out?
      1. USjordan.peoples
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload