Programerski jezik c++ :: Pc Klinika ~ Doktori za vas kompjuter

evo par tutorialsa iz blazenog c++-a:
1.
C++

I have choosen C++ because of its flexibility and ability to run on different platforms. It is based on the C language, which is in itself one of the greatest programming languages ever created.

We can start off our very first program after we get a compiler, if you are using a linux or unix os, chances are that you already have a compiler. If you are using a windows operating system, you can go to www.bloodshed.net and download the DEV compiler. It is a GUI based compiler and is very easy to use, but above all it is free. If you prefer your command line like some, you can scoot over to www.borland.com and download their text based compiler. A compiler is used to check for errors in your code and then link the program. Once we have a compiler we can move on.

#include <iostream.h>
// We are using the iostream include which is used for input and output.
int main() //This begins the program
{ //This opens the code for the program

cout << "I am starting programming" << endl; //cout prints out to the screen
cout << "Soon i will own you" << endl;

return 0; // end of the program
} // end of the program code

Ok lets examine the above, i have included the iostream include and opened the program.
I have then used the 'cout' command to print out to the screen. Whatever is between the two << << and placed between the two "" will be printed out. Remember that C and C++ programming is does not allow and mistakes, whether is be something as small as using a dot instead of a comma.

Our next program we will covering allowing input to the program using the 'cin' command.

#include <iostream.h>

int main()
{

int x,y,z; //we have declared 3 storgae boxes called 'x' 'y' & 'z' and closed the linewith ';'

cout << "This program will calculate two sums added together" << endl; // message to user
cout << "Please enter your first number" << endl;

cin >> x; //we are allowing a value for the variable callled x
cout << "Please enter your second number" << endl;

cin >> y; //we are allowing a value for the variable callled y
z = x+y; //We are declaring the value of z
cout << "The value of both numbers combined is" << z << endl;

return 0;
}

Above we have saved 3 storage boxes callled x,y and z for later use.
We then gave the user the chance to declare a value for each. They input x and y and then the value os z is set to both of them combined giving a very basic calculator that just adds the two numbers. We have saved them as integers
int x,y,z; //(and closed the variable line)

When calculating in C++ remmeber the following

+ = add
- = minus
* = muliply
/ = divide

If we wanted a figure to have a decimal place in it we would use float instead of int
Where int was int x,y,z;

If statements

We can now go onto a decision making program using the "if" command

#include <iostream.h>

int main()
{
int x;

cout <<"This program will let you know if the number you have entered is greater than 999" <<endl;
cin >> x;

if (x > 999)
{
cout << This number is greater than 999" << endl;
}

return 0;
}

Now above we have declared a storage space for 'x' and printed out to the user what the program does. We have then left them input a vlaue for 'x' and then used the if statement.
if (x > 999)
And opened the code to run should the number be greater than 999.
{
cout << This number is greater than 999" << endl;

}
And then we have closed the code for the if statement
The > sybolises is greater than

< = is less than
>= = is greater than or equal to
<= = is less than or equal to
== = is equal to
!= = is not equal to

That covers the section on basic c++ programming and concludes my guide.

2.

unction templates
Function templates are special functions that can operate with generic types. This allows us to create a function template whose functionality can be adapted to more than one variable type or class without repeating the code for each type.

This is achieved through template parameter. A template parameter is a special kind of parameter that can be used to pass a type as parameter. These function templates can use these parameters as if they were regular types.

The format for declaring function templates with type parameters is:

template <class identifier> function_declaration;
template <typename identifier> function_declaration;

The only difference between both prototypes is the use of either the keyword class or the keyword typename. Its use is indistinct since both expressions have exactly the same meaning and behave exactly the same way.

For example, to create a template function that returns the greater one of two objects we could use:

template <class myType>
myType GetMax (myType a, myType b) {
return (a>b?a:b);
}

Here we have created a template function with myType as its template parameter. This template parameter represents a type that has not yet been specified, but that can be used in the template function as if it were a regular type. As you can see, the function template GetMax returns the greater of two parameters of this still-undefined type.

To use this function template we use the following format for the function call:

function_name <type> (parameters);

For example, to call GetMax to compare two integer values of type int we can write:

int x,y;
GetMax <int> (x,y);

When the compiler encounters this call to a template function, it uses the template to automatically generate a function replacing each appearance of myType by the type passed as the actual template parameter (int in this case) and then calls it. This process is automatically performed by the compiler and is invisible to the programmer.

Here is the entire example:

// function template
#include <iostream>
using namespace std;

template <class T>
T GetMax (T a, T b) {
T result;
result = (a>b)? a : b;
return (result);
}

int main () {
int i=5, j=6, k;
long l=10, m=5, n;
k=GetMax<int>(i,j);
n=GetMax<long>(l,m);
cout << k << endl;
cout << n << endl;
return 0;
}



6
10

In this case we have used T as the template parameter name instead of myType because it is shorter and in fact is a very common template parameter name. But you can use any identifier you like.

In the example above we used the function template GetMax() twice. The first time with arguments of type int and the second one with arguments of type long. The compiler has instantiated and then called each time the appropriate version of the function.

As you can see, the type T is used within the GetMax() template function even to declare new objects of that type:

T result;

Therefore, result will be an object of the same type as the parameters a and b when the function template is instantiated with a specific type.

In this specific case where the generic type T is used as a parameter for GetMax the compiler can find out automatically which data type has to instantiate without having to explicitly specify it within angle brackets (like we have done before specifying <int> and <long>). So we could have written instead:

int i,j;
GetMax (i,j);

Since both i and j are of type int, and the compiler can automatically find out that the template parameter can only be int. This implicit method produces exactly the same result:

// function template II
#include <iostream>
using namespace std;

template <class T>
T GetMax (T a, T b) {
return (a>b?a:b);
}

int main () {
int i=5, j=6, k;
long l=10, m=5, n;
k=GetMax(i,j);
n=GetMax(l,m);
cout << k << endl;
cout << n << endl;
return 0;
}



6
10

Notice how in this case, we called our function template GetMax() without explicitly specifying the type between angle-brackets <>. The compiler automatically determines what type is needed on each call.

Because our template function includes only one template parameter (class T) and the function template itself accepts two parameters, both of this T type, we cannot call our function template with two objects of different types as arguments:

int i;
long l;
k = GetMax (i,l);

This would not be correct, since our GetMax function template expects two arguments of the same type, and in this call to it we use objects of two different types.

We can also define function templates that accept more than one type parameter, simply by specifying more template parameters. For example:

template <class T, class U>
T GetMin (T a, U b) {
return (a<b?a:b);
}

In this case, our function template GetMin() accepts two parameters of different types and returns an object of the same type as the first parameter (T) that is passed. For example, after that declaration we could call GetMin() with:

int i,j;
long l;
i = GetMin<int,long> (j,l);

or simply:

i = GetMin (j,l);

even though j and l have different types. But the compiler can determine the apropriate instantiation anyway.

Class templates
We also have the possibility to write class templates, so that a class can have members that use template parameters as types. For example:

template <class T>
class pair {
T values [2];
public:
pair (T first, T second)
{
values[0]=first; values[1]=second;
}
};

The class that we have just defined serves to store two elements of any valid type. For example, if we wanted to declare an object of this class to store two integer values of type int with the values 115 and 36 we would write:

pair<int> myobject (115, 36);

this same class would also be used to create an object to store any other type:

pair<float> myfloats (3.0, 2.18);

The only member function in the previous class template has been defined inline within the class declaration itself. In case that we define a function member outside the declaration of the class template, we must always precede that definition with the template <...> prefix:

// class templates
#include <iostream>
using namespace std;

template <class T>
class pair {
T a, b;
public:
pair (T first, T second)
{a=first; b=second;}
T getmax ();
};

template <class T>
T pair<T>::getmax ()
{
T retval;
retval = a>b? a : b;
return retval;
}

int main () {
pair <int> myobject (100, 75);
cout << myobject.getmax();
return 0;
}



100

Notice the syntax of the definition of member function getmax:

template <class T>
T pair<T>::getmax ()

Confused by so many T's? There are three T's in this declaration. The first one is the template parameter. The second T refers to the type returned by the function. And the third T (the one between angle brackets) is also a requirement. It specifies that this function's template parameter is also the class template parameter.

Template specialization
If we want to define a different implementation for a template when a specific type is passed as template parameter, we can declare a specialization of that template.

For example, let's suppose that we have a very simple class called container that can store one element of any type and that it has just one member function called increase, that increases its value. But we find that when it stores an element of type char it would be more convenient to have a completely different implementation with a function member uppercase, so we decide to declare a class template specialization for that type:

// template specialization
#include <iostream>
using namespace std;

template <class T>
class container {
T element;
public:
container (T arg) {element=arg;}
T increase () {return ++element;}
};

template <>
class container <char> {
char element;
public:
container (T arg) {element=arg;}
char uppercase ();
};

template <>
char container<char>::uppercase()
{
if ((element>='a')&&(element<='z'))
element+='A'-'a';
return element;
}

int main () {
container<int> myint (7);
container<char> mychar ('j');
cout << myint.increase() << endl;
cout << mychar.uppercase() << endl;
return 0;
}



8
J

This is the syntax used in the class template specialization:

template <> class container <char> { ... };

First of all, notice that we precede the class template name with template<>. This is a requirement in standard C++ for all template specializations, although some compilers, as an anachronism, support to declare template specialization without this prefix.

But more important than this prefix, is the <char> specialization parameter after the class template name. This specialization parameter itself identifies the type for which we are going to declare a template class specialization (char). Notice the differences between the generic class template and the specialization:

template <class T> class container { ... };
template <> class container <char> { ... };

The first line is the generic template, and the second one is the specialization.

When we declare specializations for a template class, we must also define all its members, because there is no inheritance of members from the generic template to the specialization.

Non-type parameters for templates
Besides the template arguments that are preceded by the class or typename keywords , which represent types, templates can also have regular typed parameters, similar to those found in functions. As an example, have a look at this class template that is used to contain sequences of elements:

// sequence template
#include <iostream>
using namespace std;

template <class T, int N>
class sequence {
T memblock [N];
public:
void setmember (int x, T value);
T getmember (int x);
};

template <class T, int N>
void sequence<T,N>::setmember (int x, T value) {
memblock

=value;
}

template <class T, int N>
T sequence<T,N>::getmember (int x) {
return memblock

;
}

int main () {
sequence <int,5> myints;
sequence <double,5> myfloats;
myints.setmember (0,100);
myfloats.setmember (3,3.1416);
cout << myints.getmember(0) << '\n';
cout << myfloats.getmember(3) << '\n';
return 0;
}

100
3.1416

It is also possible to set default values or types for class template parameters. For example, if the previous class template definition had been:

template <class T=char, int N=10> class sequence {..};

We could create objects using the default template parameters by declaring:

sequence<> myseq;

Which would be equivalent to:

sequence<char,10> myseq;

Templates and multiple-file projects
From the point of view of the compiler, templates are not normal functions or classes. They are compiled on demand, meaning that the code of a template function is not compiled until an instantiation with specific template arguments is required. At that moment, when an instantiation is required, the compiler generates a function specifically for those arguments from the template.

When projects grow it is usual to split the code of a program in different source code files. In these cases, the interface and implementation are generally separated. Taking a library of functions as example, the interface generally consists of declarations of the prototypes of all the functions that can be called. These are generally declared in a "header file" with a .h extension, and the implementation (the definition of these functions) is in an independent file with c++ code.

Because templates are compiled when required, this forces a restriction for multi-file projects: the implementation (definition) of a template class or function must be in the same file as its declaration. That means that we cannot separate the interface in a separate header file, and that we must include both interface and implementation in any file that uses the templates.

Since no code is generated until a template is instantiated when required, compilers are prepared to allow the inclusion more than once of the same template file with both declarations and definitions in a project without generating linkage errors.

www.devcpp.com
www.bloodshednet.com