Structure

Structure in C

Structure in c language is a user defined datatype that allows you to hold different type of elements.
Each element of a structure is called a member.
It works like a template in C++ and class in Java. You can have different type of elements in it.
It is widely used to store student information, employee information, product information, book information etc.

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Defining structure

The struct keyword is used to define structure. Let's see the syntax to define structure in c.

1. struct structure_name   
2. {  
3.     data_type member1;  
4.     data_type member2;  
5.     .  
6.     .  
7.     data_type memeberN;  
8. };  

Let's see the example to define structure for employee in c.

1. struct employee  
2. {   int id;  
3.     char name[50];  
4.     float salary;  
5. };  

Here, struct is the keyword, employee is the tag name of structure; id, name and salary are the members or fields of the structure. Let's understand it by the diagram given below:

Declaring structure variable

We can declare variable for the structure, so that we can access the member of structure easily. There are two ways to declare structure variable:

1. By struct keyword within main() function
2. By declaring variable at the time of defining structure.

1st way:
Let's see the example to declare structure variable by struct keyword. It should be declared within the main function.

1. struct employee  
2. {   int id;  
3.     char name[50];  
4.     float salary;  
5. };  

Now write given code inside the main() function.

1. struct employee e1, e2;  

2nd way:
Let's see another way to declare variable at the time of defining structure.

1. struct employee  
2. {   int id;  
3.     char name[50];  
4.     float salary;  
5. }e1,e2;  

Which approach is good

But if no. of variable are not fixed, use 1st approach. It provides you flexibility to declare the structure variable many times.
If no. of variables are fixed, use 2nd approach. It saves your code to declare variable in main() fuction.

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Accessing members of structure

There are two ways to access structure members:

1. By . (member or dot operator)
2. By -> (structure pointer operator)

Let's see the code to access the id member of p1 variable by . (member) operator.

1. p1.id  

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C Structure example

Let's see a simple example of structure in C language.

1. #include <stdio.h>  
2. #include <string.h>  
3. struct employee    
4. {   int id;    
5.     char name[50];    
6. }e1;  //declaring e1 variable for structure  
7. int main( )  
8. {  
9.    //store first employee information  
10.    e1.id=101;  
11.    strcpy(e1.name, "Sonoo Jaiswal");//copying string into char array  
12.    //printing first employee information  
13.    printf( "employee 1 id : %d\n", e1.id);  
14.    printf( "employee 1 name : %s\n", e1.name);  
15.    return 0;  
16. }  

Output:

employee 1 id : 101  employee 1 name : Sonoo Jaiswal 

Let's see another example of structure in C language to store many employees information.

1. #include <stdio.h>  
2. #include <string.h>  
3. struct employee    
4. {   int id;    
5.     char name[50];    
6.     float salary;    
7. }e1,e2;  //declaring e1 and e2 variables for structure  
8. int main( )  
9. {  
10.    //store first employee information  
11.    e1.id=101;  
12.    strcpy(e1.name, "Sonoo Jaiswal");//copying string into char array  
13.    e1.salary=56000;  
14.   
15.   //store second employee information  
16.    e2.id=102;  
17.    strcpy(e2.name, "James Bond");  
18.    e2.salary=126000;  
19.    
20.    //printing first employee information  
21.    printf( "employee 1 id : %d\n", e1.id);  
22.    printf( "employee 1 name : %s\n", e1.name);  
23.    printf( "employee 1 salary : %f\n", e1.salary);  
24.   
25.    //printing second employee information  
26.    printf( "employee 2 id : %d\n", e2.id);  
27.    printf( "employee 2 name : %s\n", e2.name);  
28.    printf( "employee 2 salary : %f\n", e2.salary);  
29.   
30.    return 0;  
31. }  

Output:

employee 1 id : 101  employee 1 name : Sonoo Jaiswal  employee 1 salary : 56000.000000  employee 2 id : 102  employee 2 name : James Bond  employee 2 salary : 126000.000000  

Array of Structures in C

There can be array of structures in C programming to store many information of different data types. The array of structures is also known as collection of structures.
Let's see an example of structure with array that stores information of 5 students and prints it.

1. #include<stdio.h>  
2. #include<conio.h>  
3. #include<string.h>  
4. struct student{  
5. int rollno;  
6. char name[10];  
7. };  
8. void main(){  
9. int i;  
10. struct student st[5];  
11. clrscr();  
12. printf("Enter Records of 5 students");  
13.   
14. for(i=0;i<5;i++){  
15. printf("\nEnter Rollno:");  
16. scanf("%d",&st[i].rollno);  
17. printf("\nEnter Name:");  
18. scanf("%s",&st[i].name);  
19. }  
20.   
21. printf("\nStudent Information List:");  
22. for(i=0;i<5;i++){  
23. printf("\nRollno:%d, Name:%s",st[i].rollno,st[i].name);  
24. }  
25.   
26. getch();  
27. }  

Output:

Enter Records of 5 students  Enter Rollno:1  Enter Name:Sonoo  Enter Rollno:2  Enter Name:Ratan  Enter Rollno:3  Enter Name:Vimal  Enter Rollno:4  Enter Name:James  Enter Rollno:5  Enter Name:Sarfraz    Student Information List:  Rollno:1, Name:Sonoo  Rollno:2, Name:Ratan  Rollno:3, Name:Vimal  Rollno:4, Name:James  Rollno:5, Name:Sarfraz  

Nested Structure in C

Nested structure in c language can have another structure as a member. There are two ways to define nested structure in c language:

1. By separate structure
2. By Embedded structure

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1) Separate structure

We can create 2 structures, but dependent structure should be used inside the main structure as a member. Let's see the code of nested structure.

1. struct Date  
2. {  
3.    int dd;  
4.    int mm;  
5.    int yyyy;   
6. };  
7. struct Employee  
8. {     
9.    int id;  
10.    char name[20];  
11.    struct Date doj;  
12. }emp1;  

As you can see, doj (date of joining) is the variable of type Date. Here doj is used as a member in Employee structure. In this way, we can use Date structure in many structures.

2) Embedded structure

We can define structure within the structure also. It requires less code than previous way. But it can't be used in many structures.

1. struct Employee  
2. {     
3.    int id;  
4.    char name[20];  
5.    struct Date  
6.     {  
7.       int dd;  
8.       int mm;  
9.       int yyyy;   
10.     }doj;  
11. }emp1;  

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Accessing Nested Structure

We can access the member of nested structure by Outer_Structure.Nested_Structure.member as given below:

1. e1.doj.dd  
2. e1.doj.mm  
3. e1.doj.yyyy  

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C Nested Structure example

Let's see a simple example of nested structure in C language.

1. #include <stdio.h>  
2. #include <string.h>  
3. struct Employee  
4. {     
5.    int id;  
6.    char name[20];  
7.    struct Date  
8.     {  
9.       int dd;  
10.       int mm;  
11.       int yyyy;   
12.     }doj;  
13. }e1;  
14. int main( )  
15. {  
16.    //storing employee information  
17.    e1.id=101;  
18.    strcpy(e1.name, "Sonoo Jaiswal");//copying string into char array  
19.    e1.doj.dd=10;  
20.    e1.doj.mm=11;  
21.    e1.doj.yyyy=2014;  
22.   
23.    //printing first employee information  
24.    printf( "employee id : %d\n", e1.id);  
25.    printf( "employee name : %s\n", e1.name);  
26.    printf( "employee date of joining (dd/mm/yyyy) : %d/%d/%d\n", e1.doj.dd,e1.doj.mm,e1.doj.yyyy);  
27.    return 0;  
28. }  

Output:

employee id : 101  employee name : Sonoo Jaiswal  employee date of joining (dd/mm/yyyy) : 10/11/2014