This document discusses various C programming concepts including macros vs functions, ANSI C standards, constants, structures, unions, enums, storage classes like automatic, external, static, and register variables, and references for further reading. It provides examples to illustrate key differences between macros and functions, declaring and initializing constants, defining and using nested structures, unions that allow storing different data types in the same variable, and static and extern storage class specifiers.

1. C_Programming
Part 7
ENG. KEROLES SHENOUDA
1

2. Macros Vs Functions
No Macro Function
1 Macro is Preprocessed Function is Compiled
2 No Type Checking Type Checking is Done
3 Code Length Increases Code Length remains Same
–
5 Speed of Execution is
Faster
Speed of Execution is Slower
6 Before Compilation macro name
is replaced by macro value
During function call , Transfer
of Control takes place
7 Useful where small code
appears many time
Useful where large code
appears many time
8 Generally Macros do not extend
beyond one line
Function can be of any number
of lines
2

3. ANSI C
 ANSI C, ISO C and Standard C refer to the successive standards for the C programming
language published by the American National Standards Institute (ANSI) and
the International Organization for Standardization (ISO). Historically, the names referred
specifically to the original and best-supported version of the standard (known as C89 or C90).
Software developers writing in C are encouraged to conform to the standards, as doing so
aids portability between compilers.
 C89
 C90
 C95
 C99
3

4. Preprocessor Test for C95 compatibility 4

5. Constant in C
 constant can be used to represent as fixed values in a C program
 Constants refers to the fixed values that do not change during the execution
of a program
5
1.const float pie =3.147;
2.const int radius =4;
3.const char c = 'A';
4.const char name[] = “C Course";

6. Constant using const keyword C
programming:
 When declaring a const variable, it is possible to put const either before or
after the type: that is, both
int const a= 15;
Or
const int x= 15;
6

7. Declare constant
 const keyword are used for declare a constant.
7
gives error
you can't modify const

8. 8

9. Structure in C
 Structure is a user defined data type which hold or store heterogeneous data item
or element in a singe variable. It is a Combination of primitive and derived data
type.
 Why Use Structure in C
 In C language array is also a user defined data type but array hold or store only similar
type of data, If we want to store different-different type of data in then we need to
defined separate variable for each type of data.
 Example: Suppose we want to store Student record, then we need to store....
 Student Name
 Roll number
 Class
 Address
9

10. Why Use Structure in C Example [without Structure] 10
It is clear that code size is
huge with respect to the
problem complexity.
Also the storage of
the single employee
information in different
arrays complicates
many operations like
entering, sorting and
printing

11.  Structures are used to collect related variables in one place. In this example all employee
information can gathered in one place. This will simplify any further operation over the
collected data, because all information items are treated as a single entity, called a
Structure.
Following format is used to define an employee structure, which is used to collect all
employee information in one place.
11

12. Structure 12
Structure is a complex data type consisting of a set of members/attributes. Each attribute
can have any data type. It can be int, float, short…its. It can be single value or array. It can
be const or variable. Also, structures may hold another structure (nested structure).
Programmers are free to define as many structures as the program required. Each structure
must be labeled with a unique label called Structure Name.
Structure Name can be used as a new data type, it can be used to define variables, it can be used to define
arrays and it can be passed to a functions.

13. Defining and Using Structure Variables 13
In above example a variable X is defined from the data type
(SEmployee). (X) variable
contains the following members (m_Name,
m_BirthDateYear,
m_BirthDateMonth, m_BirthDateDay, m_Salary).
In this example a values is
assigned to each member of (X) variable, then all members‟
values is printed.

14. Copying Structure Variable Contents to
another Variable
14

15. Employee Sort with Structures
Sort with Ages
15

16. Employee
Sort with
Structures
Sort with
Ages
16
The code
(SEmployee
employees[
100]) means
that defining
an array of 100
variable
of type
(struct
SEmployee)

17. Employee Sort with Structures
Sort with Ages
17

18. Employee Sort with Structures
Sort with Ages
18

19. With Structure Vs without Structure 19

20. Initializing Structure Variables 20

21. Nested Structure Definition
As mentioned before, it is applicable to define structure members with any data type, even
other structures type.
Structure
21
Nested Structure

22. Nested Structure 22

23. Employee Sort with Nested Structures 23

24. Employee
Sort with
Nested
Structures
24

25. Employee Sort with Nested Structures 25

26. Employee Sort with Nested Structures 26

27. Using Structures with Functions
Read and Print Employee and Date Values using Functions
27

28. Using
Structures
with
Functions
Read and Print
Employee and
Date Values
using Functions
28

29. Using
Structures
with
Functions
Read and Print
Employee and
Date Values
using Functions
29

30. Write A program Adding Two Complex
Numbers using Structure And Function
30

31. 31

32. 32

33. 33

34. enum
 An enumeration is a user-defined data type that consists of integral constants.
To define an enumeration, keyword enum is used.
34
Here, name of the enumeration is flag.
And, const1, const2,...., constN are values of type flag.
By default, const1 is 0, const2 is 1 and so on. You can change default values of enum elements
during declaration (if necessary).

35. Enumerated Type Declaration
 When you create an enumerated type, only blueprint for the variable is
created. Here's how you can create variables of enum type.
 Here, a variable check of type enum boolean is created.
 Here is another way to declare same check variable using different syntax.
35

36. Example: Enumeration Type 36
output

37. Why enums are used in C programming?
 1. Enum variable takes only one value out of many possible
values. Example to demonstrate it,
37
It's because the size of an integer is 4 bytes.
This makes enum a good choice to work with flags.
You can accomplish the same task using structures.
However, working with enums gives you efficiency along
with flexibility.

38. Why enums are used in C programming?
 More readable Here, we have added italics to our design. Note,
only code for italics is written inside if statement.
38
You can accomplish
almost anything in C
programming
without using
enumerations.
However, they can
be pretty handy in
certain situations.
That's what
differentiates good
programmers from
great programmers.

39. Example: Personal Data using Enum 39

40. Unions 40

41. Using Union
41
 Following example illustrates how to combine the three data types (int, float, double) in one
overlapped data type. Programmer is responsible on supplying and retrieving the data
correctly. If integer data is supplied, integer data must be retrieved.

42. 42

43. 43

44. 44

45. Difference between union and structure 45

46. Difference
between
union and
structure
The primary
difference can be
demonstrated by
this example:
46

47. Difference between union and structure
The primary difference can be demonstrated by this example:
 1. More memory is allocated to structures than union
 The amount of memory required to store a structure variable is the sum of memory
size of all members.
 But, the memory required to store a union variable is the memory required for the
largest element of an union.
2. Only one union member can be accessed at a time
47

48. Scope/Lifetime
 Variable “scope” refers to part of the program
that may access the variable
▫ Local, global, etc…
• Variable “lifetime” refers to time in which a
variable occupies memory
• Both determined by how and where variable is
defined
48

49. Storage classes
 In C language, each variable has a storage class which decides scope, visibility
and lifetime of that variable. The following storage classes are most oftenly
used in C programming,
 Automatic variables
 External variables
 Static variables
 Register variables

49

50. Automatic variables
 A variable declared inside a function without any storage class specification, is by
default an automatic variable. They are created when a function is called and are
destroyed automatically when the function exits. Automatic variables can also be
called local variables because they are local to a function. By default they are
assigned garbage value by the compiler.
50

51. External or Global variable
 A variable that is declared outside any function is a Global
variable. Global variables remain available throughout the entire program.
One important thing to remember about global variable is that their values
can be changed by any function in the program.
51
Here the global variable number is available to all three
functions.

52. extern keyword
The extern keyword is used before a variable to inform the compiler that this
variable is declared somewhere else.
The extern declaration does not allocate storage for variables.
52

53. Problem when extern is not used 53

54. Example Using extern in same file 54

55. Static variables
 A static variable tells the compiler to persist the variable until the end of
program. Instead of creating and destroying a variable every time when it
comes into and goes out of scope, static is initialized only once and remains
into existence till the end of program. A static variable can either be internal or
external depending upon the place of declaraction. Scope of internal
static variable remains inside the function in which it is defined. External
static variables remain restricted to scope of file in each they are declared.
 They are assigned 0 (zero) as default value by the compiler.
55

56. Static variables 56

57. Register variable
 Register variable inform the compiler to store the variable in register instead
of memory. Register variable has faster access than normal variable.
Frequently used variables are kept in register. Only few variables can be
placed inside register.
 NOTE : We can never get the address of such variables.
 Syntax :
57

58. Volatile Type Qualifier 58

59. References 59
 The Case for Learning C as Your First Programming Language
 A Tutorial on Data Representation
 std::printf, std::fprintf, std::sprintf, std::snprintf…..
 C Programming for Engineers, Dr. Mohamed Sobh
 C programming expert.
 fresh2refresh.com/c-programming
 C programming Interview questions and answers
 C – Preprocessor directives