C++ Programming Code Examples
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Make vector large enough to hold all value
/* Make vector large enough to hold all value */
#include <algorithm>
#include <functional>
#include <iomanip>
#include <iostream>
#include <list>
#include <string>
#include <vector>
using namespace std;
class PC
{
public:
enum part { keyboard, mouse, monitor };
PC( part a_part = PC::keyboard, int id = 0 );
bool operator<( const PC& rhs ) const;
void print() const;
private:
part part_;
int id_;
};
inline
PC::PC( part a_part, int id ) : part_( a_part ), id_( id ){}
inline bool PC::operator<( const PC& rhs ) const{
return id_ < rhs.id_;
}
void PC::print() const {
string component;
if( part_ == keyboard )
component = "keyboard";
else if( part_ == mouse )
component = "mouse";
else
component = "monitor";
cout << "ID: " << setw( 8 ) << left << id_ << " PC: " << component << endl;
}
int main( )
{
list<PC> listA;
listA.push_back( PC( PC::keyboard, 3 ) );
listA.push_back( PC( PC::mouse, 1 ) );
listA.push_back( PC( PC::monitor, 9 ) );
listA.push_back( PC( PC::keyboard, 2 ) );
listA.push_back( PC( PC::monitor, 8 ) );
list<PC> inspector_B( listA );
inspector_B.front() = PC( PC::mouse, 6 );
inspector_B.back() = PC( PC::monitor, 1 );
// must sort before using set algorithms
listA.sort();
inspector_B.sort();
vector<PC> result;
result.resize( listA.size() + inspector_B.size() );
}
Sort elements in container. Sorts the elements in the list, altering their position within the container. The C++ function std::list::sort() sorts the elements of the list in ascending order. The order of equal elements is preserved. It uses operator< for comparison. The sorting is performed by applying an algorithm that uses either operator< (in version (1)) or comp (in version (2)) to compare elements. This comparison shall produce a strict weak ordering of the elements (i.e., a consistent transitive comparison, without considering its reflexiveness). The resulting order of equivalent elements is stable: i.e., equivalent elements preserve the relative order they had before the call. The entire operation does not involve the construction, destruction or copy of any element object. Elements are moved within the container.
Set field width. Sets the field width to be used on output operations. The C++ function std::setw behaves as if member width were called with n as argument on the stream on which it is inserted/extracted as a manipulator (it can be inserted/extracted on input streams or output streams). It is used to sets the field width to be used on output operations. This manipulator is declared in header <iomanip>. This method accepts n as a parameter which is the integer argument corresponding to which the field width is to be set. This function returns an object of unspecified type. The setw function should only be used as a stream manipulator.
Consider a situation, when we have two persons with the same name, jhon, in the same class. Whenever we need to differentiate them definitely we would have to use some additional information along with their name, like either the area, if they live in different area or their mother's or father's name, etc. Same situation can arise in your C++ applications. For example, you might be writing some code that has a function called xyz() and there is another library available which is also having same function xyz(). Now the compiler has no way of knowing which version of xyz() function you are referring to within your code.
In C++, vectors are used to store elements of similar data types. However, unlike arrays, the size of a vector can grow dynamically. That is, we can change the size of the vector during the execution of a program as per our requirements. Vectors are part of the C++ Standard Template Library. To use vectors, we need to include the vector header file in our program. The vector class provides various methods to perform different operations on vectors. Add Elements to a Vector: To add a single element into a vector, we use the push_back() function. It inserts an element into the end of the vector. Access Elements of a Vector: In C++, we use the index number to access the vector elements. Here, we use the at() function to access the element from the specified index.
Change size. Resizes the container so that it contains n elements. The vector is a very useful class of C++ for creating the dynamic array. The size of the vector can be changed at any time to solve any programming problem. Many built-in functions exist in C++ for doing the different types of tasks in a vector container. The resize() function is one of them. It is used to change the size of the vector. The vector size can be increased or decreased by using this function. This function does not return any value. If a reallocation happens, the storage is allocated using the container's allocator, which may throw exceptions on failure (for the default allocator, bad_alloc is thrown if the allocation request does not succeed).
Inline function is one of the important feature of C++. So, let's first understand why inline functions are used and what is the purpose of inline function? When the program executes the function call instruction the CPU stores the memory address of the instruction following the function call, copies the arguments of the function on the stack and finally transfers control to the specified function. The CPU then executes the function code, stores the function return value in a predefined memory location/register and returns control to the calling function. This can become overhead if the execution time of function is less than the switching time from the caller function to called function (callee). For functions that are large and/or perform complex tasks, the overhead of the function call is usually insignificant compared to the amount of time the function takes to run. However, for small, commonly-used functions, the time needed to make the function call is often a lot more than the time needed to actually
Return size. Returns the number of elements in the list container. list::size() is an inbuilt function in C++ STL which is declared in <list> header file. size() returns the size of a particular list container. In other words it returns the number of elements which are present in a list container. This function does not accept any parameter. Function returns the number of elements in the container.
Access first element. Returns a reference to the first element in the list container. The C++ list::front function returns a reference to the first element of the list. Please note that, Unlike the list::begin function, which returns the iterator pointing to the first element, it returns the a direct reference to the same element of the list. Unlike member list::begin, which returns an iterator to this same element, this function returns a direct reference. Calling this function on an empty container causes undefined behavior.
In computer programming, we use the if statement to run a block code only when a certain condition is met. An if statement can be followed by an optional else statement, which executes when the boolean expression is false. There are three forms of if...else statements in C++: • if statement, • if...else statement, • if...else if...else statement, The if statement evaluates the condition inside the parentheses ( ). If the condition evaluates to true, the code inside the body of if is executed. If the condition evaluates to false, the code inside the body of if is skipped.
In C++, constructor is a special method which is invoked automatically at the time of object creation. It is used to initialize the data members of new object generally. The constructor in C++ has the same name as class or structure. Constructors are special class functions which performs initialization of every object. The Compiler calls the Constructor whenever an object is created. Constructors initialize values to object members after storage is allocated to the object. Whereas, Destructor on the other hand is used to destroy the class object. • Default Constructor: A constructor which has no argument is known as default constructor. It is invoked at the time of creating object.
Enumeration is a user defined datatype in C/C++ language. It is used to assign names to the integral constants which makes a program easy to read and maintain. The keyword "enum" is used to declare an enumeration. It can be used for days of the week (SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY and SATURDAY) , directions (NORTH, SOUTH, EAST and WEST) etc. The C++ enum constants are static and final implicitly. C++ Enums can be thought of as classes that have fixed set of constants.
#include is a way of including a standard or user-defined file in the program and is mostly written at the beginning of any C/C++ program. This directive is read by the preprocessor and orders it to insert the content of a user-defined or system header file into the following program. These files are mainly imported from an outside source into the current program. The process of importing such files that might be system-defined or user-defined is known as File Inclusion. This type of preprocessor directive tells the compiler to include a file in the source code program.
Access last element. Returns a reference to the last element in the list container. list::back() is an inbuilt function in C++ STL which is declared in header file. back() is used to refer to the last element of the list container. This function returns a direct reference to the last element only. When the list is empty then the function performs an undefined behaviour. Unlike member list::end, which returns an iterator just past this element, this function returns a direct reference. Calling this function on an empty container causes undefined behavior. No parameter is required.
The if...else statement executes two different codes depending upon whether the test expression is true or false. Sometimes, a choice has to be made from more than 2 possibilities. The if...else ladder allows you to check between multiple test expressions and execute different statements. In C/C++ if-else-if ladder helps user decide from among multiple options. The C/C++ if statements are executed from the top down. As soon as one of the conditions controlling the if is true, the statement associated with that if is executed, and the rest of the C else-if ladder is bypassed. If none of the conditions is true, then the final else statement will be executed.
List is a popularly used sequence container. Container is an object that holds data of same type. List container is implemented as doubly linked-list, hence it provides bidirectional sequential access to it's data. List doesn't provide fast random access, it only supports sequential access in both directions. List allows insertion and deletion operation anywhere within a sequence in constant time. Elements of list can be scattered in different chunks of memory. Container stores necessary information to allow sequential access to it's data. Lists can shrink or expand as needed from both ends at run time. The storage requirement is fulfilled automatically by internal allocator. Zero sized lists are also valid. In that case list.begin() and list.end() points to same location. But behavior of calling front() or back() is undefined. To define the std::list, we have to import the <list> header file.
Add element at the end. Adds a new element at the end of the list container, after its current last element. The content of val is copied (or moved) to the new element. This effectively increases the container size by one. The list:push_back() function in C++ STL is used to add a new element to an existing list container. It takes the element to be added as a parameter and adds it to the list container. This function accepts a single parameter which is mandatory value. This refers to the element needed to be added to the list, list_name. This function does not return any value.
A program shall contain a global function named main, which is the designated start of the program in hosted environment. main() function is the entry point of any C++ program. It is the point at which execution of program is started. When a C++ program is executed, the execution control goes directly to the main() function. Every C++ program have a main() function.
The main purpose of C++ programming is to add object orientation to the C programming language and classes are the central feature of C++ that supports object-oriented programming and are often called user-defined types. A class is used to specify the form of an object and it combines data representation and methods for manipulating that data into one neat package. The data and functions within a class are called members of the class.
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