How to Declare a Structure Variable?

Declaring a Structure Variable:

--> By defining a structure we have only created a format, the actual use of structures will be when we declare variables based on this format.

--> We declare structure variables in 2-ways:
 
       1)With Structure definition
       2)Using the Structure tag

1.With Structure definition:-

                            struct student
                            {
                                      char name[20];
                                      int rollno;
                                      float marks;
                             }stu1, stu2, stu3;

--> Here stu1, stu2, stu3 are variables of type struct "student". when we declare a variable while defining the structure template, the tagname is optional.

--> So, we can also declare them as:

                            struct
                            {
                                       char name[20];
                                       int rollno;
                                       float marks;
                             }stu1, stu2, stu3;

--> If we declare variables in this way, then we will  not be able to declare other variables of this structure type anywhere else in the program

--> So, although the tagname is optional  it is always better to specify a "tagname" for the structure.

2. Using Structure Tag:

            We can also declare structure variables using structure tag. This can be written as:

                            struct student
                            {
                                      char name[20];
                                      int rollno;
                                      float marks;
                             };
                             struct student stu1,  stu2;
                             struct student stu3;


--> Here stu1, stu2 and stu3 are structure variables that are declared using the structure tag "student".

--> Declaring a structure variable reserves "space in memory". Each structure variable declared to be of type struct student has 3 members. name, rollno, marks.

--> The "compiler" will "reserve space" for each variable sufficient to hold all the members.

Example:
 
                 each variable of type struct student will occupy 26(20+2+4) bytes.

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