C Structures

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Define Structures

In C programming, a struct (or structure) is a collection of variables (can be of different types) under a single name.

Syntax

struct structureName {
  dataType member1;
  dataType member2;
  ...
};

Example:

struct Person {
  char name[50];
  int citNo;
  float salary;
};

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Create struct Variable

When a struct type is declared, no storage or memory is allocated. To allocate memory of a given structure type and work with it, we need to create variables.

Here’s how we create structure variables:

struct Person {
  char[] name;
  int salary;
};
 
int main() {
  struct Person name = "Matteo", salary = 5000;
  return 0;
}

Another way of creating a struct variable is:

struct Person {
  char[] name;
  int salary;
} name = "Matteo", salary = 5000;

In both cases:

• person1 and person2 are struct Person variables
• p[] is a struct Person array of size 20.

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Access Members of a Structure

There are two types of operators used for accessing members of a structure.

1. . - Member operator
2. -> - Structure pointer operator (reed C Pointers and Structures)

Suppose, you want to access the salary of person2. Here’s how you can do it:

person2.salary

Example C structs:

#include <stdio.h>
#include <string.h>
 
// create struct with person1 variable
struct Person {
  char name[50];
  int citNo;
  float salary;
} person1;
 
int main() {
 
  // assign value to name of person1
  strcpy(person1.name, "George Orwell");
 
  // assign values to other person1 variables
  person1.citNo = 1984;
  person1. salary = 2500;
 
  // print struct variables
  printf("Name: %s\n", person1.name);
  printf("Citizenship No.: %d\n", person1.citNo);
  printf("Salary: %.2f", person1.salary);
 
  return 0;
}

Output:

Name: George Orwell
Citizenship No.: 1984
Salary: 2500.00

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Keyword typedef

We use the C typedef Function keyword to create an alias name for data types. It is commonly used with structures to simplify the syntax of declaring variables.

Example:

struct Distance{
  int feet;
  float inch;
};
 
int main() {
  struct Distance d1, d2;
}

We can use typedef to write an equivalent code with a simplified syntax:

typedef struct Distance {
  int feet;
  float inch;
} distances;
 
int main() {
  distances d1, d2;
}

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Example: C typedef

#include <stdio.h>
#include <string.h>
 
// struct with typedef person
typedef struct Person {
  char name[50];
  int citNo;
  float salary;
} person;
 
int main() {
 
  // create  Person variable
  person p1;
 
  // assign value to name of p1
  strcpy(p1.name, "George Orwell");
 
  // assign values to other p1 variables
  p1.citNo = 1984;
  p1. salary = 2500;
 
  // print struct variables
  printf("Name: %s\n", p1.name);
  printf("Citizenship No.: %d\n", p1.citNo);
  printf("Salary: %.2f", p1.salary);
 
  return 0;
}

Output:

Name: George Orwell
Citizenship No.: 1984
Salary: 2500.00

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Nested Structures

You can create structures within a structure in C programming.

Example:

struct complex {
  int imag;
  float real;
};
 
struct number {
  struct complex comp;
  int integers;
} num1, num2;

Suppose, you want to set imag of num2 variable to 11. Here’s how you can do it:

num2.comp.imag = 11;

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Example 3: C Nested Structures

#include <stdio.h>
 
struct complex {
  int imag;
  float real;
};
 
struct number {
  struct complex comp;
  int integer;
} num1;
 
int main() {
 
  // initialize complex variables
  num1.comp.imag = 11;
  num1.comp.real = 5.25;
 
  // initialize number variable
  num1.integer = 6;
	
  // print struct variables
  printf("Imaginary Part: %d\n", num1.comp.imag);
  printf("Real Part: %.2f\n", num1.comp.real);
  printf("Integer: %d", num1.integer);
 
  return 0;
}

Output

Imaginary Part: 11
Real Part: 5.25
Integer: 6

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