Afisare diagonale matrici

>Afiseaza elementele de pe diagonala principala, secundara, de deasupra si de dedesuptul celor 2 diagonale.

program diagonale;
var a:array[1..50,1..50] of integer;
   n,i,j:integer;
begin
    write('n=');readln(n);
    for i:=1 to n do
        for j:=1 to n do begin
           write('a[',i,',',j,']=');readln(a[i,j]);
           end;
    for i:=1 to n do begin
        for j:=1 to n do write(a[i,j], ' ');
        writeln;
        end;
    writeln('elem de deasupra diag prin:');
    for i:=1 to n-1 do begin
        for j:=i+1 to n do write(a[i,j], ' ');
        end;
    writeln;
    writeln('elem de sud diag princ:');
    for i:= 2 to n do begin
        for j:=1 to i-1 do write(a[i,j], ' ');
        end;
    writeln;
    writeln('elem de diag princ:');
    for i:=1 to n do
        for j:= 1to n do begin
             if i=j then write(a[i,j], ' ');
             end;
     writeln;
     writeln('elem de sub diag sec');
     for i:= 1 to n do
         for j:= 1 to n do begin
             if i+j>n+1 then write(a[i,j], ' ');
             end;
     writeln;
     writeln('elem de peasupra diag sec');
      for i:= 1 to n do
         for j:= 1 to n do begin
             if i+j<n+1 then write(a[i,j], ' ');
             end;
      writeln;
      writeln('elem de pe diag sec');
      for i:= 1 to n do
          for j:= 1 to n do begin
             if i+j=n+1 then write(a[i,j], ' ');
             end;
      writeln;
      readln;
 end.
{by Popescu Ionel  PascalZone.evonet.ro}