>should work but it's not, Why?

Simply because it is never null - it is an empty string. You have to check
for equality with '', probably

if(ibqRaport->Params->Columns[i]->AsString == '')

(I still don't know BCB, and don't know whether you should use == or just =)
Set

At 14:32 30.03.2001 +0200, you wrote:

>So, this code i put earlier:
>
> for(int i = 0; i < ibqRaport->Params->ColumnCount; i++)
> {
> if(ibqRaport->Params->Columns[i]->IsNull)
> {
> Application->MessageBox(AnsiString("Give me a value of param " +
> ibqRaport->Params->Columns[i]->FieldName + ".").c_str(),
> Application->Title.c_str(), MB_OK | MB_ICONEXCLAMATION);
> Abort();
> }
> }
>
>should work but it's not, Why?