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Complex data types

Complex data types. Complex data types: a data type made of a complex of smaller pieces. Pascal has four very commonly used complex data types: strings, array, records and objects.

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Complex data types

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  1. Complex data types • Complex data types: a data type made of a complex of smaller pieces. Pascal has four very commonly used complex data types: strings, array, records and objects. • We have already covered strings, will cover arrays in the next few classes and will not cover records or objects.

  2. TYPE • The reserved word TYPE introduces new types in Pascal. One new type you can define is an array. • The format of an array type definition is:TYPE IntArray = ARRAY[1..5] OF integer;This definition would produce a new type ‘IntArray’ which would consist of an array of memory locations (5 of them) which store integers.

  3. TYPE IntArray = ARRAY[1..5] OF integer; • TYPE: tells compiler we are defining a new type • IntArray: The name of the new type (name must conform to rules for naming an identifier) • ARRAY: tells compiler the new type will be an array • [1..5]: 1 will be lowest subscript; 5 will be highest. Both numbers must be same ordinal type. (Called dimensioning an array) • OF integer: means the array will store values of type integer (an array can only store one type).

  4. Once a new type is defined, you can declare a variable to hold the type like you do for a simple type. For example:VAR MyArray, YourArray: IntArray;would create two new identifiers (MyArray and YourArray) both of type IntArray. Each identifier can now hold 5 integers.

  5. How do we access the values? • To access the first value of MyArray, we would write: MyArray[1] • This would be used as any other simple variable would be used. • The 1 between the brackets is called a subscript (or index).

  6. How do we access the values (con’t) • You can also use variables or complex expressions as subscripts.For Example: MyArray[X] or MyArray[X+2] or MyArray[MyArray[2]] • This makes the array data type very powerful

  7. Out-of-range error • An out-of-range error is when you try to access an element of an array that is outside the range indicated in the declaration. • When using arrays, the compiler may not pick up on an out-of-range error.

  8. Difference between TYPE and VAR • TYPE declares a new type that you can use in the VAR section. • VAR declares a new variable of a certain type. It can be a predefined type (integer, char, etc.) or a user defined type (MyArray)

  9. Placement of type definition • In Turbo Pascal, the TYPE definition can be placed before or after the CONST definition and the VAR declaration unless an item in one of these depends on a definition in the others.CONST MaxSubscr = 20;TYPE IntArray = ARRAY [1..MaxSubsc] OF integer;VAR MarkArray: IntArray;

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