Pascal Programming Records, Stacks & Queues

Pascal Programming Record data types—a complex type that combines different data types into a single record. Sometimes called set types. The individual elements of a record are called fields or components or component fields.

Pascal Programming Each field has a name...the field identifier. The field identifiers provide a means of accessing each field in the record, similar to an array index. Each field has a type, which is established when the record is declared. The value of a record is a collection of values. There is a value in each field.

Pascal Programming The component of a record variable is a component variable.. field identifier...specifies a component variable. –e g: Business1.PresidentsLastName Though a record is a collection of values, it can sometimes be treated as a single value.

Pascal Programming So... –The record variable describes the raw record. –Record value indicates all the values in the record. –Component values indicate the field values. –Field identifiers name the fields in record.

Pascal Programming Syntax... type –Business = record –BusinessName: string[30]; –StreetAddress: string[35] –City: string[20]; –State: string[2]; –zip: integer; end;

Pascal Programming A programmer may want to structure data with a hierarchy of records. e g: –student identification –birth date and age –core courses...etc...

Pascal Programming Records for a group may be read into an array. Thus, we see that... – data structures are a means of organizing, storing and manipulating data. How do we chose which structure to use? –Everything being equal, chose the one that can be understood and worked with most easily.

Pascal Programming If all items are of the same type...a single array of that type works best. If items differ in type, use an array of records. Or, use parallel arrays.

Pascal Programming with statements... With provides instruction(s) to carry out an operation. Syntax –with record_variable_list do statement (usually compound) The records_variable_list is separated by commas.

Pascal Programming Stacks and Queues The stack, a specialized data structure, compares to a stack of shoe boxes. New data goes into a box on the top of the stack. To read from the stack, access the first box, discard it, read the second box, discard it etc....

Pascal Programming Stacks serves the purpose of reversing the order of data -- first in, last out. e g: stacktop = (TopValue) This creates a decrementation of the stack. The text illustrated using the stack to match parenthesis. Find and save a left parenthesis then look for the right one, eliminate all characters in between. Cry fowl when a left parenthesis occurs again without a right one.

Pascal Programming Queue... A data structure for first in/first out data handling. The opposite of the stack. Like a waiting line...first come...first served. A queue can be implemented so that as the array empties and reaches the end the beginning fills again. It becomes circular.

Pascal Programming Pascal Sets Sets contain data like a list but that data is unordered. To use sets in a variable, we use set types The ordinals in the sets are its elements. These are the Base_type of the set.

Pascal Programming Example type –Grade = set of ; constant –superior: grade = [ ] The first illustrates the declaration of a set and the second the appending of a typed constant.