This document discusses structures and unions in C programming. It defines structures as a way to group dissimilar data types and define a new data type. Structures use the struct keyword and allow defining custom data types. Unions are similar to structures but can only store one data element at a time, with storage size equal to the largest member. The document provides examples of declaring and defining structures and accessing structure members using dot and arrow operators. It also discusses static and extern storage classes.

1. STRUCTURES AND
UNIONS
Instructor
Dhiviya Rose J , AP-Sr. Scale | SoCSE

2. Recap
2

3. Problem 1
• Storing the 5 subject marks for 10 students in a class
60 40 60 80 100
60 55 60 80 100
10 76 60 78 100
10 66 10 10 80
80 100 10 10 80
80 100 60 40 80
10 40 80 40 60
10 40 100 100 60
10 40 100 56 60
10 40 100 80 80
int marks[10][5]

4. Problem 2
• Storing the 5 subject marks for 10 students in a class
NAVJEET
SINGROHA 60 40 60 80 100 68
ABHISHEK
ANAND 60 55 60 80 100 71
ADITYA JUYAL 10 76 60 78 100 64.8
AMIT PANDEY 10 66 10 10 80 35.2
ANANDITA
SINGH 80 100 10 10 80 56
ANIRUDH
PUROHIT 80 100 60 40 80 72
ANTRIKSH
SINGH 10 40 80 40 60 46
ANUBHA TYAGI 10 40 100 100 60 62
ANUSHKA
YADAV 10 40 100 56 60 53.2
ARPIT SINGH 10 40 100 80 80 62

5. Definition : Structure
• Group of dissimilar Datatypes
• Defines a new type
• a new kind of data type that compiler regards as a single unit
• User Defined datatype
• Uses struct keyword to create

6. Example

7. Structure Declaration

8. Example – Structure Declaration
• Creates a structure datatype named motor

9. Structure Variable Declaration
• Creating variable of structure type
• Two ways as structure variable
• With structure declaration
• Using structure tag
• As structure pointer

11. Accessing Members of Structure

12. Method 1 : Using . operator
struct ADate {
int month;
int day;
int year;
};
struct ADate date;
date.month = 1;
date.day = 19;
date.year = 2017;
OR

14. Method 2 : Using ->operator
struct Date {
int month;
int day;
int year;
};
Date d1;
Date *d=&d1;
d->month = month;
d->day = day;
d->year = year;

15. Structures inside Structures
Example
struct COST { int amount;
char currency_type; }
struct PART { struct COST cost;
char id[2];
int num_avail;
}

16. Unions
• Differ in memory allocation.
• In Structure its “AND” and in Unions its “XOR”
• Accessing remains the same as structures
union sample {
float avg;
int rollno;
char *name;
};
/* either a float xor an int xor a string */

17. Definition
• Like Structures Unions can stores disimilar data elements
in a group.
• But you can store only one data element at a time.
• Once a new value is assigned to any member value the
older one is erased.
• Storage size of union is the size of its largest member

20. STORAGE CLASSES

21. Need???
• defines the scope (visibility)
• life time of variables
• storage classes used in a C Program
• auto
• register
• static
• extern

22. Auto Storage Class
• auto is the default storage class for all local variables.
{
int Count;
auto int Month;
}
• The example above defines two variables with the same
storage class. auto can only be used within functions, i.e.
local variables.

23. Register Storage Class
• Used to define local variables
• Stored in Register instead of RAM
• Maximum size equal to register size
• Eg. Frequently used variables like counter
{
register int Miles;
}

24. Static Storage class
• provides a lifetime over the entire program,
• declared with the keyword static
• variables are automatically initialized to zero
• static int a;
• They continue to exist even after the block in which they
are defined terminates.
• storage allocated becomes permanent for the duration of
the program.

25. Extern Storage Class
• extern is used to give a reference of a global variable that
is visible to ALL the program files.
• extern int a;

26. INFO106 COMPUTER
PROGRAMMING

27. Summary of Units
1. Introduction
2. C Programming Basics
3. Arrays and Strings
4. Functions and Pointers
5. Structure and Unions

28. Future Enhancement
• Working with our own header files
• Embedded C
• Other Programming Languages

29. Comparison of PL

30. Embedded C example

31. cont….