Structures
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Outline

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
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Introduction
Structure Definitions and Declarations
Initializing Structures
Operations on Structures Members
Structures as Functions Parameters
Array of Structures
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Introduction

Structures
 Collection of related data items called components (or
members) that are NOT necessarily of the same data type.
 Commonly used to define records to be stored in files.
 Usually the collections of related data item are
characteristics in an object
 For example:
Object
Characteristics
Book
Car
Student
price, number of pages, year published
price, year, model, colour
name, matric_no, semester
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Structure Definition

Syntax:
 struct StructureTypeName
{
structure member declaration list
};
Example:
struct book
{
float price;
int numpages;
int year;
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};
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Structure Definition

struct information
 A struct cannot contain an instance of itself
 Can contain a member that is a pointer to the
same structure type
 A structure definition does not reserve space in
memory
 Instead creates a new data type used to define
structure variables
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Structure Declaration

After defining a structure type, we may declare
variables that are of that type. A structure
variable declaration requires these elements :
keyword struct
 structure type name
 a list of variables names separated by commas
 concluding semicolon
E.g. struct book book1;

struct book my_book,his_book,her_book;
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How does it look like in my
program?
#include <stdio.h>
struct book
{
float price;
int numpages;
int year;
};
int main( )
#include <stdio.h>
struct book
{
float price;
int numpages;
int year;
} book1;
or
{
struct
……
}
book
book1;
int main( )
{
……
}
struct book book1;
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Initializing Structures
struct book book1 = {25.50, 690, 2005};
OR
book1.price = 25.50;
book1.numpages = 690;
book1.year = 2005;
dot operator
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Operations on Structures
Members
Operation
Normal variable
Structure member
Read from user
scanf(“%f”, &price);
scanf(“%f”, &book1.price);
Assign value
price = 25.50;
book1.price = 25.50;
Print as output
printf(“%f\n”, price);
printf(“%f\n”, book1.price);
Copy to a
variable
newprice = price;
newprice = book1.price;
Pass value to a
function
if(fun1(price) > 5)
if(fun1(book1.price) > 5)
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Multiple Structures Variables
struct book my_book, his_book, her_book;
 price
 numpages
 year
my_book
 price
 numpages
 year
his_book
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 price
 numpages
 year
her_book
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Multiple Structures Variables
e.g.
struct book my_book, his_book, her_book;
my_book. price = 25.50;
her_book.price = 10.50;
if(my_book.price > her_book.price)
printf(“My book is more expensive than hers\n”);
else
printf(“My book is cheaper than hers\n”);
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Sample Program
#include <stdio.h>
struct book
{
float price;
int numpages;
int year;
};
int main()
{
struct book my_book = {25.50,690,2005};
struct book her_book;
printf("Enter book price : ");
scanf("%f", &her_book.price);
printf("Enter number of pages : ");
scanf("%d", &her_book.numpages);
printf("Enter year published : ");
scanf("%d", &her_book.year);
printf("My book :\n");
printf("%.2f\t%d\t%d\n", my_book.price,
my_book.numpages, my_book.year);
printf("Her book :\n");
printf("%.2f\t%d\t%d\n", her_book.price,
her_book.numpages, her_book.year);
if(my_book.year > her_book.year)
printf("My book is the latest publication\n");
else
printf("Her book is the latest publication\n");
return 0;
}
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Structures as Function Parameters


Like variables of any other data type,
structure variables can be used as
formal and actual function parameters.
In passing structure variables by value
to a function, the operating systems
makes a copy of the entire structure in
the data area of the called function.
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Structures as Function Parameters
……
float compute_price(struct book bk);
…
int main( )
{ struct book bookC;
……………
new_price = compute_price(bookC);
……
}
float compute_price(struct book bkC)
//function prototype
//function call
//function definition
{ …….
bkC.price=bkC.price + tax;
……
return(bkC.price);
}
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Structures as Function Parameters
A nonvoid function of a structure type can return a structure of that
structure type under the function’s name if we use a return statement
in the function.
struct book read ();
//function prototype

int main( )
{ ……….
struct book b;
b = read( );
//function call
……….
}
struct book read( )
//function definition
{ struct book bk;
printf(“Enter price:”);
scanf(“%f”, &bk.price);
…..
return(bk);
}
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Structures as Function Parameters


If all members of a structure variable are not needed for a function to
perform its task, we can pass only the required members.
However, we must specify structure members using the component
selection operator.
int modify_year(int a, int b, int year);
//function prototype
……..
int main( )
{ struct book bkC;
…………….
avg_year=modify_year(aa, bb, bkC.year); //function call
…….
}
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Structures as Function Parameters

It is possible to pass structure variables using pointers
int main()
{ struct book b;
………
read(&b); //function call
}
void read(struct book *bk)
{
printf(“Enter price:”);
scanf(“%f”, &bk->price);
printf(“Enter numpages:”);
scanf(“%d”, &bk->numpages);
…….
}
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struct book read()
{
struct book her_book;
Sample Program
#include <stdio.h>
struct book {
float price;
int numpages;
int year;
};
struct book read();
void print(struct book, struct book);
void compare(int, int);
int main()
{
struct book my_book = {25.50,690,2005};
struct book she_book;
she_book=read();
print(my_book , she_book);
compare(my_book.year, she_book.year);
return 0;
}
printf("Enter book price : ");
scanf("%f", &her_book.price);
printf("Enter number of pages : ");
scanf("%d", &her_book.numpages);
printf("Enter year published : ");
scanf("%d", &her_book.year);
return(her_book);
}
void print(struct book my_book, struct book her_book)
{
printf("My book :\n");
printf("%.2f\t%d\t%d\n", my_book.price,
my_book.numpages, my_book.year);
printf("Her book :\n");
printf("%.2f\t%d\t%d\n", her_book.price,
her_book.numpages, her_book.year);
}
void compare(int my_year, int she_year)
{
if(my_year > she_year)
printf("My book is the latest publication\n");
else
printf("Her book is the latest
publication\n");
}
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An Array of Structures

Suppose a company has 50 full-time employees.
struct employeeType
{
char firstName[20];
char lastName[20];
int personID;
char deptID[10];
double yearlySalary;
double monthlySalary
double yearToDatePaid;
double monthlyBonus;
};
struct employeeType employees[50];
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How it looks like
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How to access??
int counter;
for(counter = 0; counter < 50; counter++)
{
scanf(“%s %s %d %s %lf”,
&employees[counter].firstName,
&employees[counter].lastName,
&employees[counter].personID,
&employees[counter].deptID,
&employees[counter].yearlySalary);
employees[counter].monthlySalary =
employees[counter].yearlySalary/12;
employees[counter].yearToDatePaid = 0.0;
employees[counter].monthlyBonus = 0.0;
}
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How to access??

Suppose that for a given month the monthly bonuses are
already stored in each employee’s record, and we have to
calculate the monthly paycheck and update the yearToDatePaid
amount. The following loop computes and prints the employee’s
paycheck for the month:
double payCheck; //variable to calculate the paycheck
for(counter = 0; counter < 50; counter++)
{
printf(“%s %s”, employees[counter].firstName,
employees[counter].lastName);
payCheck = employees[counter].monthlySalary +
employees[counter].monthlyBonus;
employees[counter].yearToDatePaid =
employees[counter].yearToDatePaid + payCheck;
}
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Arrays in Structures

Example
const arraySize = 5;
struct listType
{
int listElem[arraySize];
int listLength;
};
struct listType list;
//array containing the list
//length of the list
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How it looks like

struct listType
listElem
listLength
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Structure Within a Structure
struct nameType
{
string first;
string middle;
string last;
};
struct addressType
{
string address1;
string address2;
string city;
string state;
string zip;
};
struct dateType
{
string month;
string day;
string year;
};
struct contactType
{
string phone;
string cellphone;
string fax;
string pager;
string email;
};
struct employeeType
{
struct nameType name;
string emplID;
struct addressType address;
struct dateType hiredate;
struct dateType quitdate;
struct contactType contact;
string deptID;
double salary;
};
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Structure Within a Structure :
How to access??
//variable declaration
struct employeeType newEmployee;
//declare 100 employees' records
struct employeeType newEmployee[100];
newEmployee.salary = 45678.00;
newEmployee.name.first = "Mary";
newEmployee.name.middle = "Beth";
newEmployee.name.last = "Simmons";
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Structure Within a Structure :
How to access??

The statement
scanf(“%s”, &newEmployee.name.first);
reads and stores a string into
newEmployee.name.first.

The statement
newEmployee.salary = newEmployee.salary * 1.05;
updates the salary of newEmployee
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