1. A union is a block of memory that can hold different data types and only stores the data of its last written member. 2. The document demonstrates using unions to store different data like a dish name and price by assigning them separately. 3. It also shows defining a structure with members like start year, department code, and ID number and initializing them separately.

1. Another Way to Collect Dissimilar Data

2. What Is a Union?
• a block of memory that is used to hold data items of different
types.
– Declaring Unions & Defining Union Variables
union automobile {
int year;
char model[8];
int engine_power;
float weight;} sedan, pick_up, sport_utility;
– Referring a Union with . or ->
sedan.year = 1997;
union automobile *ptr; ptr->year = 1997;

3. Ex1:
/* 20L01.c Referencing a union */
#include <stdio.h>
#include <string.h>
main(void)
{
union menu {
char name[23];
double price;
} dish;
printf("The content assigned to the union separately:n");
/* reference name */
strcpy(dish.name, "Sweet and Sour Chicken");
printf("Dish Name: %sn", dish.name);
/* reference price */
dish.price = 9.95;
printf("Dish Price: %5.2fn", dish.price);
return 0;
}

4. Ex2:
#include <stdio.h>
main(void)
{
union employee {
int start_year;
int dpt_code;
int id_number;
} info;
/* initialize start_year */
info.start_year = 1997;
/* initialize dpt_code */
info.dpt_code = 8;
/* initialize id */
info.id_number = 1234;
/* display content of union */
printf("Start Year: %dn", info.start_year);
printf("Dpt. Code: %dn", info.dpt_code);
printf("ID Number: %dn", info.id_number);
return 0;
}

5. /* 20L03.c The size of a union */
#include <stdio.h>
#include <string.h>
main(void)
union u {
double x;
int y;
} a_union;
struct s {
double x;
int y;
} a_struct;
printf("The size of double: %d-byten",
sizeof(double));
printf("The size of int: %d-byten",
sizeof(int));
printf("The size of a_union: %d-byten",
sizeof(a_union));
printf("The size of a_struct: %d-byten",
sizeof(a_struct));
return 0;
}

6. Defining Bit Fields with struct
• a structure have their own memory locations.
struct tag_name {
data_type name1: length1;
data_type name2: lenght2;
. . .
data_type nameN: lengthN;
} variable_list;

7. struct horse
{
int age;
int height;
char name[20];
char father[20];
char mother[20];
};
struct horse Dobbin = {
24, 17,"Dobbin", "Trigger", "Flossie"
};
struct horse Trigger = {
30, 15, "Trigger", "Smith", "Wesson"
};
Accessing Structure Members
Dobbin.age = 12;

8. #include <stdio.h>
int main(void)
{
/* Structure declaration */
struct horse
{
int age;
int height;
char name[20];
char father[20];
char mother[20];
};
struct horse My_first_horse; /* Structure variable declaration */
/* Initialize the structure variable from input data */
printf("Enter the name of the horse: " );
scanf("%s", My_first_horse.name ); /* Read the horse's name */
printf("How old is %s? ", My_first_horse.name );
scanf("%d", &My_first_horse.age ); /* Read the horse's age */
printf("How high is %s ( in hands )? ", My_first_horse.name );
scanf("%d", &My_first_horse.height ); /* Read the horse's height */
printf("Who is %s's father? ", My_first_horse.name );
scanf("%s", My_first_horse.father ); /* Get the father's name */
printf("Who is %s's mother? ", My_first_horse.name );
scanf("%s", My_first_horse.mother ); /* Get the mother's name */
/* Now tell them what we know */
printf("n%s is %d years old, %d hands high,",
My_first_horse.name, My_first_horse.age, My_first_horse.height);
printf(" and has %s and %s as parents.n", My_first_horse.father,
My_first_horse.mother );
return 0;
}

9. /* 20L06.c: Applying bit fields */
#include <stdio.h>
#include <string.h>
struct bit_field {
int cable: 1;
int dish: 1;
};
struct survey {
char name[20];
struct bit_field c_d;
int age;
int hour_per_week;
union {
char cable_company[16];
char dish_company[16];
} provider;
};
void DataEnter(struct survey *s);
void DataDisplay(struct survey *s);
main(void)
{
struct survey tv;
DataEnter(&tv);
DataDisplay(&tv);
return 0;
}
/* function definition */
void DataEnter(struct survey *ptr)
{
char is_yes[4];
printf("Are you using cable at home? (Yes or No)n");
gets(is_yes);
if ((is_yes[0] == `Y') ||
(is_yes[0] == `y')){
printf("Enter the cable company name:n");
gets(ptr->provider.cable_company);
ptr->c_d.cable = 1;
ptr->c_d.dish = 0;
} else {
printf("Are you using a satellite dish? (Yes or No)n");
gets(is_yes);
if ((is_yes[0] == `Y') ||
(is_yes[0] == `y')){
printf("Enter the satellite dish company name:n");
gets(ptr->provider.dish_company);
ptr->c_d.cable = 0;
ptr->c_d.dish = 1;
} else {
ptr->c_d.cable = 0;
ptr->c_d.dish = 0;
}
}
printf("Please enter your name:n");
gets(ptr->name);

10. printf("Your age:n");
scanf("%d", &ptr->age);
printf("How many hours you spend on watching TV per week:n");
scanf("%d", &ptr->hour_per_week);
}
/* function definition */
void DataDisplay(struct survey *ptr)
{
printf("nHere's what you've entered:n");
printf("Name: %sn", ptr->name);
printf("Age: %dn", ptr->age);
printf("Hour per week: %dn", ptr->hour_per_week);
if (ptr->c_d.cable && !ptr->c_d.dish)
printf("Your cable company is: %sn",
ptr->provider.cable_company);
else if (!ptr->c_d.cable && ptr->c_d.dish)
printf("Your satellite dish company is: %sn",
ptr->provider.dish_company);
else
printf("You don't have cable or a satellite dish.n");
printf("nThanks and Bye!n");
}