comp size with expression

hi@all
i´m looking for an expression to set the comp sice (with and high) to a new
value. i have to do that with lots of compositions and mayby i have to change it
later. i have found this with and high parameters under the expression menue but
it won´t work for me.
sorry for bad english

o.k. i thought that. therefore i have looked in this skripting-dialog, and try
to understand how it works, its difficult.
can you tell me what i have to write for this step: i will set the composition
size to 730

"thiscomp width = 730"

This simple script will set the width of all the comps in your project to 730:

for (var i = 1; i <= app.project.numItems; i++){
  if (app.project.item(i) instanceof CompItem){
    app.project.item(i).width = 730;
  }
}

That should give you the idea.