Structure
Structure
• So far we have seen a variables whose data types are very simple.
They are a numbers of wither integer or float point with a specific
range.
• There types of variables, who only have a single value to their name,
are known as basic variable or primitives,
• Sometime it is advantageous to group common variables in to a single
collection. For example a date would require a day, month and year.
• Array is a data structure which holds multiple numbers of objects having
the same basic property(data types) in a contiguous memory slots.
• It is possible to reserve contiguous memory space for aggregates of
elements of different data types each. A data type which is created to
reserve such type of memory space is called user defined data type.
• Structure definition is a user defined variable type which is a grouping of
one or more variables. Structure definition could be a date which may be
made up of three int members.
• Before creating a structure variable you must create a structure
definition.
Defining structure
• Is giving a compiler a blue print for creating your type.
• Note: when you create a variable of any kind, you must give it a
unique name that is different than its type.
• Syntax
struct structname
{
datatype1 variable1;
datatype2 variable2;
};
• Writing a structure definition begins with the word struct flowed by
the type to be and ended with a structure block that is ultimately
terminated with a semicolon.
• Within the structure block you declare all the member variables you
want associated with that type but don’t try to initialize them.
• The data members (synonym for member variables) of a structure
won’t be created until a variable based on the structure is crated. It is
just a description of a storage unit.
• That storage unit isn’t reserved until you create a variable with it.
• Structure definition has the same type of scoping as a variable.
• Example: defining a structure Struct date
struct student {
{ int day;
int id; int month;
char name[15]; int year;
}; };
Declaring and using struct data types
• Once you have defines a structure you can create a variable from it
just as you would any other variable.
date birthday;
• The above declaration statement would create a variable called
birthday whose type is the structure date. The variable contains three
parts: day, month and year.
What is the difference between the following
int I;
student std1;
Initializing structure variables
• To initialize a structure variable's members, you follow the original
declaration with the assignment operator[=].
• Next you will define an initialization block which is a list of initializers
separated by commas and enclosed in curly braces.
• Lastly, you end it with a semi colon.
• These values are assigned to member variables in the order that they
occur.
Examples
date nco_birthday ={19,8,1979};
student std1 ={“Abebe”,”RTCH-0000/00”};
• The first one creates a variable called nco_birthday and initializes it to a list of
values.
• If you try to assign more values then are the member variable, you will get a
compiler error.
• It is possible to use any expressions that you normally would, but the expression
must result in a value.
int myday = 19;
int mymnoth = 5;
date nco_birthday = {myday, mymonth+3, 2001-22};
• date nco_birthday ={19,8,1979};
Is not equal to the following
• date nco_birthday;
• nco_birthday ={19,8,1979};
• You must access each member individually;
Accessing members of a structure variable
• You can use a member variable in any place you’d use a normal
variable, but you must specify it by the structure variable’s name as
well as the member variable’s name using the member operator.
• To specify that you want a member of a specific structure variable,
you use the structure member operator which is the period(dot).
• Use the structure’s name, follow with the period and end with the
member.
• EXAMPLES!
Variable with Definition
• The syntax of struct also allows you to create variables based on a
structure definition without using two separate statements.
struct {
struct
inttagx,y;
{
}point;
member(s),
Has 2 members.
=
}variable;
B.c. the structure definition is not named it cannot be used
• Example:
elsewhere a point
to create variable
a variable of right after
the same the type.
struct pointtag structure is defined:
struct pointtag
struct pointtag {
int x,y;
{ };
int x,y;
}point; pointtag point;
Possible options
struct pointtag
struct pointtag
{ {
int x,y; int x,y;
}point1,point2; }point1={0,0},point2{0,0};
Array of struct
• What if lots of lists are neede?
END
