C_ProgrammingPart 7

ENG. KEROLES SHENOUDA

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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

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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

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Preprocessor Test for C95 compatibility 4

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

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1.const float pie =3.147;

2.const int radius =4;

3.const char c = 'A';

4.const char name[] = “C Course";

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;

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Declare constant const keyword are used for declare a constant.

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gives error

you can't modify const

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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

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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 complicatesmany operations like

entering, sorting and

printing

Structures are used to collect related variables in one place. In this example all employeeinformation can gathered in one place. This will simplify any further operation over thecollected 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 allemployee information in one place.

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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.

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.

Copying Structure Variable Contents to another Variable

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Employee Sort with StructuresSort with Ages

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Employee Sort with StructuresSort with Ages

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The code

(SEmployee

employees[

100]) means

that defining

an array of 100

variable

of type

(struct

SEmployee)

Employee Sort with StructuresSort with Ages

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Employee Sort with StructuresSort with Ages

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With Structure Vs without Structure 19

Initializing Structure Variables 20

Nested Structure DefinitionAs mentioned before, it is applicable to define structure members with any data type, evenother structures type.

Structure

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Nested Structure

Nested Structure 22

Employee Sort with Nested Structures 23

Employee Sort with Nested Structures

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Employee Sort with Nested Structures 25

Employee Sort with Nested Structures 26

Using Structures with FunctionsRead and Print Employee and Date Values using Functions

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Using Structures with FunctionsRead and Print Employee and Date Values using Functions

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Using Structures with FunctionsRead and Print Employee and Date Values using Functions

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Write A program Adding Two Complex Numbers using Structure And Function

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enum

An enumeration is a user-defined data type that consists of integral constants. To define an enumeration, keyword enum is used.

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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).

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.

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Example: Enumeration Type 36

output

Why enums are used in C programming?

1. Enum variable takes only one value out of many possible values. Example to demonstrate it,

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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.

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.

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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.

Example: Personal Data using Enum 39

Unions 40

Using Union41

Following example illustrates how to combine the three data types (int, float, double) in oneoverlapped data type. Programmer is responsible on supplying and retrieving the datacorrectly. If integer data is supplied, integer data must be retrieved.

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Difference between union and structure 45

Difference between union and structureThe primary difference can be demonstrated by this example:

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Difference between union and structureThe 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

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Scope/Lifetime

Variable “scope” refers to part of the programthat may access the variable▫ Local, global, etc…• Variable “lifetime” refers to time in which avariable occupies memory• Both determined by how and where variable isdefined

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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 oftenlyused in C programming,

Automatic variables

External variables

Static variables

Register variables

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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.

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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.

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Here the global variable number is available to all three

functions.

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.

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Problem when extern is not used 53

Example Using extern in same file 54

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.

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Static variables 56

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 :

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Volatile Type Qualifier 58

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