Introduction to c ++ part -2

• What is the difference between c and
c++?
• What is a class?
• What is an object?
• What are cin,cout ?
Recall

Introduction to C++
File handling ,Operator Over loading
Week 4 day 2

File Handling
• C++ provides the following classes to
perform output and input of characters
t to/from files:
– ofstream: Stream class to write on files
– ifstream: Stream class to read from files
– fstream: Stream class to both read and write
from/to files.

Open a file
int main ()
{
ofstream myfile;
myfile.open ("example.txt");
myfile.close();
return 0;
}
Class Name

Open a file
int main ()
{
ofstream myfile;
myfile.close();
return 0;
}
Object Name

Open a file
int main ()
{
ofstream myfile;
myfile.close();
return 0;
}
Method named open() is used
to open a file.
It takes 2 parameter.
1) file name
2) File Mode (optional)

Open a file
int main ()
{
ofstream myfile;
myfile.close();
return 0;
}
Method named close() is used
to close a file.

Open a file
 ios:in : Open for input operations.
 ios::out : Open for output operations.
 ios::ateSet : The initial position at the end of
the file.
 ios::app : All output operations are performed at
the end of the file, appending the content to the
current content of the file.
 ios::trunc : If the file opened for output
operations already existed before, its previous
content is deleted and replaced by the new one.

Writing to the file
int main ()
{
ofstream myfile; myfile.open("example.txt");
if (myfile.is_open())
{
myfile << "This is a line.n";
myfile.close();
}
else cout << "Unable to open file";
return 0;
}
//is_open() returns true if the
object point to opened file

Writing to the file
int main ()
{
ofstream myfile; myfile.open("example.txt");
{
myfile << "This is a line.n";
myfile.close();
}
return 0;
}
Writing to the file

Reading from File
int main ()
{
string line; ifstream myfile; myfile.open("example.txt");
{
myfile>>line;
cout << line << “n”;
myfile.close();
}
return 0;
}
Return single word from
the file to the variable
line

Reading from File
int main ()
{
string line; ifstream myfile; myfile.open("example.txt");
{
while ( getline (myfile,line) )
{
}
myfile.close();
}
return 0;
Return single line from
the file to the variable in
the argument

Why Operator Overloading?
• The meaning of operators are already defined
and fixed for basic types like: int, float, double
etc in C++ language. For example: If you want to
add two integers then, + operator is used. But,
for user-defined types(like: objects), you can
define the meaning of operator
• Readable code
• Extension of language to include user-defined
types
• I.e., classes
• Make operators sensitive to context

18
Simple Example
class complex {
public: double real, imag;
}
• I wish if I could do something as below
complex a,b,c;
a.real=12; a.imag=3;
b.real=2; b.imag=6;
c = a + b;
c = a-b;
c = a*b ;
I.e., would like to write
ordinary arithmetic expressions
on this user-defined class.

#include<iostream>
class complex
{
public: int real,imaginary;
complex add(complex ob)
{
complex t;
t.real=real+ob.real;
t.imaginary=imaginary+ob.imaginary;
return(t);
}
};
int main()
{
complex obj1,obj2,result;
obj1.real=12; obj2.imaginary=3;
result=obj1.add(obj2); //how if i could simply be result=obj1+obj2
cout<<result.real<<result.imaginary;
return 0;
}
Real =12
Imaginary =3
Complex add(obj)
{
t.real=12+obj.real;
t.imaginary=3+obj.imaginary;
Return t;
}
Real =8
Imaginary =1
Complex add(obj)
{
t.real = 8+obj.real;
Return t;
}
obj1
obj2

Operator Overloading CS-2303, C-Term 2010 20
General Format
returnType operator+(parameters);
  
any type keyword operator symbol
• Return type : may be whatever the
operator returns
• Operator : is the keyword to be used for
anyoverloading
• Operator symbol : may be any over loadable
operator from the list.

#include<iostream>
class complex
{
public: int real,imaginary;
complex operator+(complex ob)
{
complex t;
t.imaginary=imaginary+ob.imaginary;
return(t);
}
};
int main()
{
result=obj1+obj2 // result=obj1.operator+(obj2);
cout<<result.real<<result.imaginary;
return 0;
}
Real =12
Imaginary =3
Complex operator+(obj)
{
t.real=12+obj.real;
Return t;
}
Real =8
Imaginary =1
Complex operator+(obj)
{
t.real = 8+obj.real;
Return t;
}
obj1
obj2

Questions?
“A good question deserve a good
grade…”

Self Check
• What are ifstream, ofstram,
fstream?
–A function to operate file
–Structure type pointer to the file
–A class

Self Check
• Where is is_open() defined?
–Class called ifstream/ofstream/fstream
–Iostream.h
–In the File

Self Check
• I want to write “Hello baabtra” in
to a file
ofstream myfile;
myfile.open("example.txt");
{
myfile << “Hello baabtra";
myfile.close();

Self Check
• From previous program i want to
store “hello” in a varaible
string line;
ifstream myfile;
myfile.open("example.txt");
{
myfile>>line;
myfile.close();
}

Self Check
• Act of taking more than one form
with same name is called
–Function overloading
–Operator overloading
–Inheritance
–polymorphism

Self Check
• Act of taking more than one form
with same name is called
–Function overloading
–Operator overloading
–Inheritance
–polymorphism
“Function overloading and operator overloading are implementation or examples of
polymorphism”

class complex
{
public: int real,imag;
complex operator+(complex ob)
{
complex t;
t.imag=imag+ob.imag;
return(t);
}
};
int main()
{
obj1.real=12; obj2.imag=3;
obj2.real=8; obj2.imag=1;
result=obj1+obj2
cout<<result.real<<result.imag;
return 0;
}
Self Check
Complete the below

Introduction to c ++ part -2

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Introduction to c ++ part -2