Page 159 - DCAP507_SYSTEM_SOFTWARE

Unit 10: Programming Languages Concept (I)

X,Y, Z : VALUE; Notes
W: LETTER;
Thus defined variables RESULT and answer can have values from 1 to 100, similarly X,Y, Z, can
have from 2 to 15 and W can have from the list : 'A', 'B', 'C', … 'Z'.

The typedef Statement

In addition to creating new data types, C allows both standard and user-defined data types to be
renamed using typedef statement. The syntax is:
Typedef data - type data - identifier
New name

Predefined data-type
Reserved word

Example:
Typedef float REAL;
Makes the name REAL a synonym for float. The name REAL can now be used in place of the term
float. For example, the declaration
REAL val;
The typedef does not create a new data type; it creates a new name for an existing data type.
The #define statement is used to create synonym for an existing data type Similarly # define
preprocessor command is used to equate constants and operators to create symbolic names.

Example:
#define PI 3,1416 - equate symbolic name PI to the number 3.1416.
#define TIMES * - equates symbolic name TIMES to the operator *. The substitutions are
made by the C preprocessor just prior to program compilation. The symbolic name is referred
to as a macro.

10.3.3 Structure Data Types

Structure data types are formed from primitive data types. Arrays, Records, Files are examples
in PASCAL and Arrays, Structures, Unions, Files in C language. Records, Structures & Unions,
etc., are discussed in the following section.

The RECORD and STRUCTURE

A collection of related data items (or fields), treated as a unit, is called a record. Whereas a set of
related records is referred to as a file. To understand this concept, suppose a file of students at a
NDIMCRC centre having data items registration no. (reg.no.), name , course & telephone.

Since array can have data-items only of identical type, the above information can be stored in
record type structure. So in record type structure, one can store related the data-items which are
distinct in nature and type.

LOVELY PROFESSIONAL UNIVERSITY 153