how to have modal dialog in c#?

[pinoywebdev]

I am launching an exe (child) from a main exe (parent)

the parent exe is in c++

the child exe is in c#

in child exe, i have a code

thisApp.showdialog() // this causes the child's UI to be shown

however, the child dialog is not modal... while it is up, i can click away from it and access the parent window

how to have a modal dialog with the above setup?