CC213-Week08-User-Defined Data Types.pptx

User-Defined Data Types
(struct-enum-union)
Week 08
CC213:Programming Applications

Agenda
 Structures
 What is a structure?
 Using structures
 Structure and Functions
 Structure and Pointers
 Structure and Arrays
 Nested Structures
 Enumeration
 Union

Structure is the collection of variables of different types
under a single name for better handling.
Examples:
• you may want to store information about a student:
id & gpa
• you may also want to store information about a person:
name, citizenship number and salary.
 Keyword struct is used for defining a structure.
What is a Structure?

1. Define the structure.
2. Declare/Initialize instances/variables of the structure.
3. Access members of an instance of the structure.
Using Structures

Syntax:
struct structure_name
{ data_type member1;
data_type member2;
.
.
data_type memeber;
};
1.Defining a Structure
Example:
struct Student
{ int id;
float gpa;
};
Name of data type

 When a structure is defined, it creates a user-
defined data type but, no storage is allocated.
 Example: variables can be declared from Person
structure as following:
2.Declaring Structure Variables
struct Person
{ char name[50];
int cit_no;
float salary;
};
Inside/outside main function:
struct Person p1, p2, p[20];
struct Person
{ char name[50];
int cit_no;
float salary;
}p1 ,p2 ,p[20];
Single
Variables
declaration
Array of
Variables declaration
Name of data type

 There are two types of operators used for
accessing members of a structure:
3.Accessing Members of a
Structure Variable
• Syntax: structure_variable_name.member_name
• Example, to access salary member via variable p2:
p2.salary=100;
2.Structure pointer operator( )
1.Member operator(.)
• Syntax: structure_pointer_name->member_name
• Example, to access salary member via pointer ptr:
Person * ptr; ptr=&p2;
ptrsalary=200;

1. Manipulating individual component
 Example: strcpy(current_planet.name, "Jupiter");
current_planet.diameter = 142980;
current_planet.moons = 16;
current_planet.orbit_time = 11.9;
current_planet.rotation_time = 9.925;
2. Manipulating whole structure
 Example: previous_planet = current_planet;
Extra Examples: Manipulating
a structure

 Programmer generally use typedef while defining
structures in C language. For example:
Defining a Structure using the
Keyword typedef
Syntax:
typedef struct
{ data_type member1;
data_type member2;
.
.
data_type memeber;
} structure_name;


Example1:
typedef struct
{ int imag;
float real; } Complex;
Inside/Outside main function:
Complex c1,c2;
 Here, typedef keyword is used for creating a type
Complex (which is of type as struct Complex). Then,
two structure variables c1 and c2 are created by
this Complex type.
Name of data type

Example 2:
typedef struct{
char name[10];
double diameter;
int moons;
double orbit_time, rotation_time;
}Planet_t;
int main (void)
{
int x;
Planet_t current_planet;
Planet_t previous_planet;
planet_t blank_planet = { " ", 0, 0, 0, 0};
float y;
return 0;
}


1.
2.
In C, structure can be passed as input parameter
To functions by two methods:
Passing by value (passing actual value as argument)
Passing by reference (passing address of an argument)
Structure and Functions

#include<stdio.h>
struct Student{
char name[50];
int roll;
};
void Display (struct Student stu);
int main()
{struct Student s1;
printf("Enter student's name:");
scanf("%s",s1.name);
printf("Enter roll number:");
scanf("%d",&s1.roll);
Display(s1);
return0;
}
void Display(struct Student stu)
{ printf("OutputnName:%s",stu.name);
printf("nRoll:%d",stu.roll);}
Output
Enter student's name: Kevin
Enter roll number: 149
Output
Name: Kevin
Roll: 149
Example1:
Passing structure by value

void print_planet(Planet_t *pa)
{
printf("%sn", pa->name); //you need to use ->
printf("the diameter is: %f kmn", pa->diameter);
printf("number of moons : %d n", pa->moons);
printf("orbit time is : %f yearsn", (*pa).orbit_time); //you can use *
also
}
void main()
{
planet_t current_planet = { "pluto", 15, 7, 13, 10};
print_planet(&current_planet);
}
Example2:
Passing structure by reference
• The following function receive structure as a reference
parameter to print out its contents:

Planet_t get_planet(void)
{
planet_t planet;
planet.name,
&planet.diameter,
&planet.moons,
&planet.orbit_time,
&planet.rotation_time);
}
void main()
{
scanf("%s%lf%d%lf%lf",
return(planet);
Planet_t current_planet;
current_planet = get_planet();
}
Example3: A function that
returns a structure

 Set of named integer constants that specifies all the
legal values that a variable of its type can have.
-Example:
enum Color {red, white, blue}
//or alternatively:
//typedef enum {red, white, blue} Color;
//in main function: define and initialize an enum variable:
Color c;
c = red;
c = white;
Enumeration

 The key point to understand about an
enumeration that each of the symbols stands
for an integer value and can be used in any
integer expression.
Enumeration

#include <stdio.h>
int main()
{
enum Days{Sunday,Monday,Tuesday,Wednesday,Thursday,Friday,Saturday};
Days theDay;
int j = 0;
printf("Please day of the week (0 to 6)n"); scanf("%d",&j);
theDay = Days(j);
if(theDay == Sunday || theDay == Saturday)
printf("Hurray it is the weekendn");
else
printf("still at work ");
return 0;
}
Enumeration

Union
union Student {
int id;
float gpa;
char name[20];
};
int main( ) {
union Student x;
printf( "Memory size occupied by x union variable: %dn", sizeof(x));
return 0;
}
//output:
Memory size occupied by data :
20
• Union is similar to structure in definition. However, the
memory allocated for a union variable is shared between
union members and the size allocated is equal to the largest
member size.
• Example1:

Example2:
#include <string.h>
union Student {
int id;
float gpa;
char name[20];
};
int main( ) {
union Student x;
x.id = 10; //will use the 20 bytes
x.gpa = 3.5; //will use the same 20 bytes
strcpy( x.name, “Hassan Ahmed"); //will use the same 20 bytes
printf( “x.id : %dn", x.id);
printf( “x.gpa: %fn", x.gpa);
printf( “x.name : %sn", x.name);
return 0;
}
//output:
x.id : 1917853763
x.gpa :
4122360580327794860452759994368.000000
x.name : Hassan Ahmed

Example3:
#include <stdio.h>
#include <string.h>
union Student {
int id;
float gpa;
char name[20];
};
int main( ) {
union Student x;
x.id = 10;
printf( “x.id : %dn", x.id);
x.gpa = 3.5;
printf( “x.gpa : %fn", x.gpa);
strcpy( x.name, “Hassan Ahmed");
printf( “x.name : %sn", x.name);
return 0;
}
//output
x.id : 10
x.gpa : 3.500000
x.name : Hassan Ahmed

CC213-Week08-User-Defined Data Types.pptx

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