Structures of C and typedef of structures

The  concept structures of C and typedef struct in C is covered in this blog

Structures(records) in C

A structure is a group of variables of different data types and An array is a collection of variables of the same data types

Suppose if we have an array of 6 elements. then, it is not allowed to store 2 int , 2floats, 2char elements in an array.

if we have a struct of 6 elements. then, it is allowed to store 2int, 2floats, 2char elements in a struct

With C language, we can store similar data types with Arrays and String

to store different data types in a single name we use a keyword called struct

why  we use structures

suppose we want to store a record of an employee

employee_name(string) employee_no(int) employee_salary(float)

to store an employee record we need to store into 3 individual array’s and it’s better to use one array of structure

Syntax

structure Declaration

Initialization of structure

Structure elements can not be initialized with the declaration

Structure elements can be initialized by using braces { }

Accessing structure elements

Access structure elements by using  .operator

#include<stdio.h>
int main()
{
    struct employee
    {
        char name[12];
         float salary;
          int employee_no;
    };
    struct employee e1 ={"tom",5000.45,1884};
    printf("%s %f %d",e1.name,e1.salary,e1.employee_no);
return 0;
}

Output

tom
5000.45
1884

writing and reading a structure variable

#include <stdio.h>
#include <stdlib.h>
int main()
{
    struct num
    {
        int x, y, z;
    }s;
    FILE *fp;
    s.x=25;
    s.y=50;
    s.z=100;
    fp=fopen("sample.txt","wb");
    fwrite(&s, sizeof(s),1,fp);
    fclose(fp);
    fp =fopen("sample.txt", "rb");
    fread(&s, sizeof(s),1,fp);
    printf("\nx=%d\ny=%d\n z= %d",s.x,s.y,s.z);
    fclose(fp);
    return 0;
}

Output

x=25
y=50
z=100

Typedef

Keyword typedef is used to assign a duplicate name to datatypes

Why typedef is used?

Syntax

Typedef  datatype  duplicate_name;

#include <stdio.h>
#include<string.h>
int main()
{
  typedef  char string[10];
     string x ="hello"; //string[10] is replaced with string x
    int i;
    for(i=0;i<10;i++)
    {
        printf("%c",x[i]);
    }
    return 0;
}

Output

hello

Typedef of structures

Another way of declaring a structure is by using typedef

 the main advantage of typedef of a structure is you no need to mention struct keyword every time you initialize a structure

we just need to specify the typedef in front of struct tag to create a new type

Example

#include<stdio.h>
typedef struct employee_record {
   char name[20];
   float salary;
   int employee_no;
}emp;
emp e1 = {"tom",5000.45,1884};
int main()
{
    printf("\nName of the employee : %s",e1.name);
    printf("\n employee salary : %f",e1.salary);
    printf("\n employee_no : %d",e1.employee_no);
    return(0);
}

Output

name of the employee is tom
employee salary 5000.45
employee_no: 1884