Exercise correction
```delphi
program tableau ;
uses crt;
type T_tab = array [ 1..20 ] of integer ;
var tnbre : T_tab; i, grd : integer ;
begin
for i := 1 to 20 do
begin
repeat
writeln ( 'entrez votre nombre :' );
readln ( tnbre [i] );
until tnbre [i] > 0;
end;
grd := tnbre [1];
for i := 2 to 20 do
begin
if ( grd < tnbre [i] ) then
begin
grd := tnbre [i];
end;
end;
writeln('le plus grand élément est :', grd);
readkey;
end.
```
program tableau ;
uses crt;
type T_tab = array [ 1..20 ] of integer ;
var tnbre : T_tab; i, grd : integer ;
begin
for i := 1 to 20 do
begin
repeat
writeln ( 'entrez votre nombre :' );
readln ( tnbre [i] );
until tnbre [i] > 0;
end;
grd := tnbre [1];
for i := 2 to 20 do
begin
if ( grd < tnbre [i] ) then
begin
grd := tnbre [i];
end;
end;
writeln('le plus grand élément est :', grd);
readkey;
end.
```