Pascal insert user input to an array

Question

I am trying to get better at functional programming. As a start I am planning on trying out with couple of languages like Pascal, Scheme, ML etc. First I started with Pascal. I am trying to insert user input into a integer array in pascal and then get them reverse.

  1 program ReverseList;
  2 
  3 var
  4         i: Integer;
  5         k: Integer;
  6         a: array[1..100] of Integer;
  7 begin   
  8         i := 0;
  9         repeat  
 10                 writeln('Enter a number');
 11                 readln(k);
 12                 if k > -1 then 
 13                         i := i + 1;
 14                         a[i] := k;
 15         until(k < 0);
 16         for i := 1 to i do    
 17                 writeln(a[i]);
 18 end.

In past I have mostly been a java developer so I was so custom to using all the lists thats available. Also ideally I was wondering if I can build a list where I can iterate over the list based on the number of elements in that list.

It would be great if anyone could point me on the direction of good tutorials in functional programming as well as syntax on above mentioned programming languages.

Good to know didn't know that was a critical factor, I ll keep that in mind going forward. Thanks. — add-semi-colons
– add-semi-colons, Commented Sep 25, 2011 at 18:15
I have given points and verbally thank using comments but didn't realized about the acceptance. — add-semi-colons
– add-semi-colons, Commented Sep 25, 2011 at 18:45
@evilone, its not the key point. I agree that it is fair to give credit to those who have helped you, but, you still aren't required to do so. — Toon Krijthe
– Toon Krijthe, Commented Sep 25, 2011 at 18:50
@Null-Hypothesis, if you want more answers from other people, its maybe better not to answer (and accept) your own question. If you have the correct solution and you don't want any more answers, you can provide the answer yourself. — Toon Krijthe
– Toon Krijthe, Commented Sep 26, 2011 at 19:00

Toon Krijthe · Accepted Answer · 2011-09-25 18:21:47Z

2

There are several problems with your program:

The array is not initialized.
There is no input checking, both i=0 and i>100 result in an illegal array index.
The array index and the value are the same, is that correct?
You only write the first 10 numbers (but you use a different index, which is certain to be out of range).
The output is not in reverse.

There are also several pascal tutorials.

By the way, Pascal isn't a functional language. So if you really want to learn a functional language, you better try another one (like Lisp, Ml or probably F#).

answered Sep 25, 2011 at 18:21

Toon Krijthe

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2 Comments

add-semi-colons Over a year ago

I actually updated the code section of the question after your comment. Now I have a list printing and working on the reverse. Thanks much.

Marco van de Voort Over a year ago

Gamecat: he said learning functional programming, not learning function language :-)

add-semi-colons · Accepted Answer · 2011-09-26 01:45:39Z

It was a good practice and I managed to figure a solution for this. I am sure there are better ways to do, and also this doesn't look like I am using the functionalities of functional programming. But if anyone wants to provide a better solution please do so,

{author: Null-Hypothesis}

program ReverseList;

var
        i: Integer; {integer to keep the array length}
        k: Integer; {user input value}
        a: array[1..100] of Integer; {array to store the user inputs}
begin
        i := 0;
        repeat  {iterate until user input is negative or number of inputs exceed array size}

                writeln('Enter a number or enter negative value to exit the program.');
                readln(k);
                if(k > -1) and (i < 100) then   {check for negative value and size of the array}
                begin
                        i := i + 1;     {increase array index}
                        a[i] := k       {assign value to array}
                end
                else
                        break;  {exit if array size exceed the limit of array}
        until(k < 0);
writeln;

{Printing the user input before the reversing the list}
writeln('Original order of the list');
for i := 1 to i do
        writeln(a[i]);
writeln;

{Printing the reverse list}
writeln('Reversed List');
for i := i downto 1 do  {decrement array index}
        writeln(a[i]);
writeln('Bye!!!');
end.

Happy Coding, off to the next language...

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