Structure in C Programming

Introduction to structures

We know that an array is a collection of similar data items such as int, float, char etc. If more number of Data items of same data type are grouped, we normally use arrays. For example, the marks of 6 students can be stored using array as shown below:

Int marks[6]={86,99,95,93,87,91};

The ordinary variables and arrays can handle variety of situations. But, in real world, we often deal with entities that are collection of dissimilar data types. For example, suppose we want to have the data related to a student. We may be interested in:

• Name of the student            (char array, string type)
• Roll number                        (int type)
• Average marks                    (float type)

Note that the above data is a collection of various items of dissimilar data types(heterogeneous). So, arrays cannot be used (because, array is a collection of similar data types, homogeneous in nature). This is where, the structure are used.

Structure and its definition

Now, we shall see “ what is a structure? What is the syntax of a structure?”
Definition : A structure is defined as a collection of logically related (generally heterogenous) Variables under a single name. All these variables may contain data items of similar or dissimilar

Data types. Using these variables each item of a structure can be selected. Each variable in the

Structure represents an item and is called member or field or element of the structure. Each field

Has a type.

The general format or syntax of a structure is shown below:

Where

• Struct is keyword which tells the compiler that a structure is being defined.
• Member1, member2,… are called members of the structure. They are also called fields or Elements of the structure.
• The members are declared within curly braces. It is called body of the structure. The Members can be any of data types such as int, char, float etc.
• There should be semicolon at the end of closing brace.

Example: Structure definition for storing student data.
Assume the student data consists of the following:

•    Name of the student: Name is made up of sequence of characters. Ex: “Jecob Lefore”
•    Roll number: It is of type integer Ex:1101
•    Average marks: It is of type float Ex: 93.45

Since the above information is related to student and all the above information is logically related to
A student, we can use the structure. The structure definition to hold the information of student is
Shown below:
                               Struct student
                               {
                                          Char name [10];
                                          Int    rollno;
                                          Float   avg;
                             };
In the above example, observe the following points:

• Struct is the keyword.
• Student is called the name of the structure. The name of the structure is also called structure tag.
• Name, rollno and avg are called fields of the structure. They are also called members of Structure and are associated with data types char, int and float.

The structure definition does not reserve any space  in memory for the members. So, it is called a  structure template and memory will  not be allocated for the template. This is pictorially represented as shown below:

                                                          
Note : the various items in a structure can be same or different data types. But, all the items should be logically related. Do not combine un-related data.

For example, for the above structure definition, let us have filed number_of_wheels. The field number_of_wheels is in no way related to student data and hence has to  be avoided.