Declaration and Initialization of structure in c

5 min 25 sec read Basic

Array in C does not allow storing data elements of a different kind whereas Structures allows storing data elements of a different kind. Structure in C is a user-defined data type that allows you to store data elements of a different kind.

 

Why Structure is used?

 

Suppose you want to store the information of students in a college, with attributes like Name, Roll No, Age, and Gender. So, Name should be defined with a datatype "String", and Age should be defined with a datatype "Integer". Here you clearly understand the difference between Arrays and Structures. In Arrays, you can only store elements of one type either Names of "String" Datatype or Ages of "Integer" Datatype whereas in Structures you can store both. That�s the magic of structures.

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Declaration of structure in c 

The following example shows how to declare a Structure in C using the struct keyword:

Syntax:-

struct [structure Name]
 {
  datatype variable;
  datatype variable;
  ...
  datatype variable;
 } [one or more structure variables];

"structure Name" is an "Optional" Name that is used to define a structure.

"datatype variable" is simply declaring a normal variable int a; float per;

"[one or more structure variables]" is an "Optional" Name that is used to define one or more structure variables.

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Example:-

struct Student
 {
  char name[20]; 
  int   age;
 } student; 

 

Accessing structure members in c 

 

Dot Operator (.) also known as member access operator is used to access structure members in C.

The following example clears the concept:-

#include <stdio.h>
#include <string.h>

struct Students
{
    char name[20];
    int   age;
};

int main( )
{
    /* Declare firstStudent of type Students */
    struct Students firstStudent;
    /* Declare secondStudent of type Students */
    struct Students secondStudent;
    
    /* firstStudent specification */
    strcpy( firstStudent.name, "Jazzy");
    firstStudent.age = 23;
    
    /* secondStudent specification */
    strcpy( secondStudent.name, "Steven");
    secondStudent.age = 22;
    
    /* print firstStudent info */
    printf("First Student Name: %s
",   firstStudent.name);
    printf("First Student age: %d
", firstStudent.age);
    
    
    /* print secondStudent info */
    printf("Second Student Name : %s
", secondStudent.name);
    printf("Second Student age : %d
",secondStudent.age);
    
    return 0;
}

Output:-

First Student Name: Jazzy
First Student age: 23
Second Student Name: Steven
Second Student age: 22

 

How to pass Structure as Function Argument?

 

How do we pass a normal variable to a function?
e.g: add(5,3) , swap(6,5)
Similarly, we can pass structure variables to function .

Example :-

#include 
#include 

struct Students {
    char  name[50];
    int  age;
 };

/* function declaration */
void display( struct Students student );

int main( ) {
    
    struct Students firstStudent;       
    struct Students secondStudent;        
    
    /* Student 1 specification */
    strcpy( firstStudent.name, "Manish");
    firstStudent.age = 23;
    
    /* Student 2 specification */
    strcpy( secondStudent.name, "Nitesh");
    secondStudent.age = 24;
    
    /* print FirstStudent info */
    display( firstStudent );
    
    /* Print Student2 info */
    display( secondStudent );
    
    return 0;
}

void display( struct Students student ) {
    
    printf( "Name : %s
", student.name);
    printf( "Age : %d
", student.age);
}

Output :-

Name : Manish
Age : 23
Name: Nitesh
Age : 24

How to pass a struct by reference in c?

To pass a struct by reference in C, You can define pointers to structures in the same way as you define pointers to any other variable

struct Students *pointer_Struct;

Now, you can store the address of a structure variable in the above-defined pointer variable. To find the address of a structure variable, place the &; operator before the structure's name as follows

pointer_Struct = &firstStudent;

To access the members of a structure using a pointer to that structure, you must use the? operator as follows

Example:-

pointer_Struct->name;

#include <stdio.h>
#include <string.h>

struct Students {
    char  name[50];
    int  age;
 };

/* function declaration */
void display( struct Students *student );

int main( ) {
    
    struct Students firstStudent;        
    struct Students secondStudent;        
    
    /* Student 1 specification */
    strcpy( firstStudent.name, "Manish");
    firstStudent.age = 23;
    
    /* Student 2 specification */
    strcpy( secondStudent.name, "Nitesh");
    secondStudent.age = 24;
    
    /* print FirstStudent info */
    display( &firstStudent );
    
    /* Print Student2 info */
    display( &secondStudent );
    
    return 0;
}

void display( struct Students *student ) {
    
    printf( "Name : %s
", student->name);
    printf( "Age : %d
", student->age);
}

Output:-

Name : Manish
Age : 23
Name : Nitesh
Age : 24

 

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