Wrong output of bubble sort algorithm in Pascal

March 30, 2023

Recently I have been trying to create a bubble sort algorithm in Pascal language, however after the program is run, the output turned out to be only 0s and 1s. I wonder what have I done wrong.

program BubbleSort;

const n = 9;
var
    arr : array [0..n] of integer;
    num, a, b, i, j, temp : integer;
begin
    temp := 0;
    for a := 0 to n do
    begin
        writeln('Please enter the ', a, '-th element in the array:');
        readln(arr[a]);
    end;
    for i := 0 to (n - 1) do
    begin
        for j := 0 to (n - i - 1) do
        begin
            if (arr[j] > arr[j + 1]) then
            begin
                arr[j] := temp;
                arr[j] := arr[j + 1];
                arr[j + 1] := temp;
            end;
        end;
    end;
    writeln('The sorted array is as follows:');
    for b := 0 to n do
    begin
        write(arr[b], ' ');
    end;
end.

Since I am familiar with C# and Java, I tried my best to declare the array to start from index 0, and that might be the cause of the problem. I have no idea.

>Solution :

The problem lies in the swapping of the elements in the array. You’re not correctly swapping the values of arr[j] and arr[j + 1]. Instead, you’re overwriting arr[j] with temp (which is 0) and then assigning arr[j + 1] to temp, effectively losing the original value of arr[j].

Here’s the corrected version of the swapping code in your bubble sort algorithm:

if (arr[j] > arr[j + 1]) then
begin
    temp := arr[j];
    arr[j] := arr[j + 1];
    arr[j + 1] := temp;
end;

With this change, your complete Pascal code for the bubble sort should look like:

program BinarySearch;

const n = 9;
var
    arr : array [0..n] of integer;
    a, b, i, j, temp : integer;
begin
    temp := 0;
    for a := 0 to n do
    begin
        writeln('Please enter the ', a, '-th element in the array:');
        readln(arr[a]);
    end;
    for i := 0 to (n - 1) do
    begin
        for j := 0 to (n - i - 1) do
        begin
            if (arr[j] > arr[j + 1]) then
            begin
                temp := arr[j];
                arr[j] := arr[j + 1];
                arr[j + 1] := temp;
            end;
        end;
    end;
    writeln('The sorted array is as follows:');
    for b := 0 to n do
    begin
        write(arr[b], ' ');
    end;
end.