Aillianna

Verified answer

Const
    handsfree = false;

var
    matrix: array[1..100, 1..100] of real;
    sum, a, b: real;
    i, j, n, k: integer;

begin
    {ввод матрицы}
    if handsfree then begin
        n := random(20) + 2;
    end
    else begin
        write('n =');
        readln(n);
    end;
    
    writeln('Matrix data:');
    for i := 1 to n do
    begin
        for j := 1 to n do
            if handsfree then begin
                matrix[i, j] := random(100) - 50;
                write(matrix[i, j]:4, ' ')
            end
            else
                read(matrix[i, j]);
        writeln;
    end;
    
    {сумма, произведение, пр. агригаты}
    write('Enter a, b =');
    readln(a, b);
    sum := 0;
    k := 0;
    for i := 1 to n do
        if (matrix[i, i] >= a) and (matrix[i, i] <= b) then {если нужен фильтр}
        begin
            sum := sum + matrix[i, i];
            k := k + 1;
        end;
    
    if k > 0 then
        writeln('Average (selected) = ', sum / k)
    else writeln('Such elements not found');
end.