C/AL prog..problems

I have four fields 1 postal code 2 city 3 street 4 house no now, i want the user to select a postal code from a non editable list,now once the postal code is selected the cities that are assigned the postal code selected should be shown in the list. similarly the streets are to be filtered and then house numbers… i donnt want to set a tablerelation to do this task.what i need is all task done by coding.i can use the command button. (is it some thing what the attain doesnt provides…?) aks

declare a record variable for city table and then filter the table on postal code and run the form FORM.RUN(22,rec);