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Lesson 7
STRUCTURE: PUTTING RELATED ITEMS TOGETHER
When writing a program, several variables
(identifiers) are declared and used. Some of the names used as identifiers
are related and can be grouped together (memory wise) in one location as one
unit in memory. This grouping of related names, including several variables
and functions is called a structure. In C, structures group only
variables, while in C++ structures group variables as well as their related
functions. Each variable and function is referred to as a member of
the structure. In C++, the bundling of variables and functions adds the
important concept of Object Oriented Programming (OOP), also known as class,
to the C language. This incorporation of variables and functions makes
C++ both a Procedural as well Object-Oriented language.
HOW TO CREATE A STRUCTURE IN C
The key word struct is used to create a
structure. In C, there are three general formats to create a structure
variable as shown in Figures 7.1a, b, and c. Notice in Figure 7.1a, the
structure is defined with the use of a tag name followed by the definition
of the structure and the actual structure variable name. In Figure 7.1b, the
use of a tag name is eliminated and the rest of the definition and the
structure declaration remain the same.
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1.
struct tagname {
2.
datatype variablename;
3.
datatype variablename;
4.
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5.
·
6.
} structurevariablename;
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1.
struct {
2.
datatype variablename;
3.
datatype variablename;|
4.
·
5.
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6.
} strucuturevariablename;
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Figure 7.1a – The definition and declaration
of a structure with the use of a tag name following the struct
keyword.
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Figure 7.1b – The definition and declaration
of a structure without the use of the tag name following the struct
keyword.
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1.
struct tagname {
2.
datatype variablename;
3.
datatype variablename;
4.
·
5.
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6. };
7. struct
tagname structurevariablename;
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Figure 7.1c – The definition and declaration
of a structure with the use of the tag name following the struct
keyword in both the definition and the declaration.
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