#include guards

Practical session #2

Software Engineering 094219

Modular programming

Header file = interface Declarations of functions and classes. Definitions of classes, constants and

types. Inline functions.

CPP file = implementation Definitions of functions (class members

or regular functions ). Initialization of static class members. In order to use the identifiers from

header file – it must be included.

#include Pre-compiler command that inserts the

included file in place of #include. #include <filename> - standard library #include “filename.h” - your own header

file

#include - rule 1

typedef my_int* int_vector;//Needs my_int but has no //such include

File1.h

typedef int my_int;…..

File2.h

#include “File2.h”#include “File1.h”

Usage1.cpp

OKCompilation

error!

#include “File1.h”#include “File2.h”

Usage2.cpp

Every header file must have all #includes it requires !!!Otherwise the order of includes will matter and the files are not independent!

#include - a problem

#include “File1.h”#include “File3.h”//Needs code C and B

Usage1.cpp

Compilation error!Redefinition of class

A

“File2.h” is included twice ! => class A is defined twice !

class A { };//More code

File2.h

#include “File2.h”//Code C

File1.h

#include “File2.h”//Code B

File3.h

#include - a solution

#include “File1.h”#include “File3.h”//Needs code C and B

Usage1.cpp

OK

#ifndef FILE2_H#define FILE2_Hclass A { };//More code#endif

File2.h

#include “File2.h”//Code C

File1.h

#include “File2.h”//Code B

File3.h

Include guards

Every header file should have include guards ! To avoid double or cyclic inclusion!

These files should have

include guards too !

C++ variables and types

Agenda

Variables and types

Reference

10

Variable

Variable is a place (a piece of memory) for data storage, in C++: variable=object.

Variable has a name = identifier. Variable has a type, that determines:

The size in memory. The values that can be stored in it. The operations that can be applied to it.

Variables should be initialized (good practice ). Initialization syntax: type identifier (initial_value) ; //example: int

k(5); type identifier = initial_value; //example: int k

= 5; 11

The sam

e

Example:double num

( 0.0 );

Types in C++

12

1. Primitive types. Examples:

bool, int, double, char…

2. Compound (or composite ) types: Any type that is not primitive. Any type that made up of primitive types or

other compound types. Examples:

Arrays., Pointers, references, Classes, And there are more…

C++ is a statically typed language each variable has to have a type before usage and this type cannot be changed!

Primitive built-in types

Minimum size

Meaning Type

NA Boolean bool

8 bits Character char

16 bits Wide character wchar_t

16 bits Short integer short

16 bits Integer int

32 bits Long integer long

32 bits (6 p) Single-precision floating point

float

64 bits (10 p) Double-precision floating point

double

128 bits (10 p) Extended-precision floating point

long double

13

We can find out the actual size of a

variable by using sizeof operator

Scope and local variable The scope (or simply the “{ }” braces) of an identifier, is the part

of the program over which the identifier can be seen and used.

Local variable is a variable which defined inside a function. Local variable can be accessed only from the scope where it was defined and cleared automatically at the end of the scope.

Example (with compiler errors): 1. void average()2.{3. for ( int i =0 ; i < 5 ; i++ ){4. int x , sum = 0 ;5. std::cout << “Enter "<< i+1 <<"'th integer:“ << std::endl;

6. std::cin >> x ;7. sum += x ;8. }9. std::cout<<" The average: “<< sum / i <<std::endl;10.}

What is the error and

how can we fix it?

14

Global variable defined in the main scope – outside the scope of all functions/classes.

Examples:

1. #include <iostream>2. //Global scope3. int x = 20;4. void incX(){//Local scope5. // int x = 10 ; 6. x ++;7. }8. int main(){9. std::cout<<" Global x = "<< x <<std::endl;10. incX();11. std::cout<<" Global x + 1 = "<< x <<std::endl; 12. system("pause");13. return 0 ;14.}

Global variable

What will be the result of adding this

code line (5)?

15

Constant (const) variable

Constant (const) variable must be initialized at its definition point and cannot be changed after its definition.

Example: 1. void main(){2. const int cInt = 5 ;3. const double cDoub ; //ERROR4. cInt ++ ; //ERROR5. cDoub += .3 ; // ERROR6. std::cout << cInt << std::endl ;7. system("pause");8. }16

Agenda

Variables and types

Reference

17

Reference variable

Reference type can be thought as alternative name for a variable.

Reference must be initialized at definition time. Example:

1. long index = 10 ;2. long &refIndex = index ;3. std::cout<< ++refIndex << endl; 4. std::cout<< index << endl;5. long &refIndex2 ; //ERROR6. long &refIndex3 = 10 ; //ERROR

Reference can’t be rebind after definition.

refIndex is a reference to index forever. Whenever we use refIndex (after we created it) we access the object referenced. 18

const reference

Reference can be const: you cannot change the object via the const reference.

long longNum ; const long& longRef = longNum; //correct longRef = 5; //ERROR

The opposite is not correct: const object can have only const references or pointers to it

const long longNum (5); long& longRef = longNum; // ERROR.

//Because we could change const object //via non const reference!19