C++ Programming Code Examples
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Use a map to create a phone directory: string class
/* Use a map to create a phone directory: string class */
#include <iostream>
#include <map>
#include <string>
using namespace std;
class name {
string str;
public:
name() {
str = "";
}
name(string s) {
str = s;
}
string get() {
return str;
}
};
// Define less than relative to name objects.
bool operator<(name a, name b){
return a.get() < b.get();
}
class phoneNum {
string str;
public:
phoneNum() {
str = "";
}
phoneNum(string s) {
str = s;
}
string get() {
return str;
}
};
int main()
{
map<name, phoneNum> directory;
directory.insert(pair<name, phoneNum>(name("J"), phoneNum("999-1111")));
directory.insert(pair<name, phoneNum>(name("C"), phoneNum("999-2222")));
directory.insert(pair<name, phoneNum>(name("J"), phoneNum("555-3333")));
directory.insert(pair<name, phoneNum>(name("T"),phoneNum("4444")));
// given a name, find number
string str;
cout << "Enter name: ";
cin >> str;
map<name, phoneNum>::iterator p;
p = directory.find(name(str));
if(p != directory.end())
cout << "Phone number: " << p->second.get();
else
cout << "Name not in directory.\n";
return 0;
}
Maps are associative containers that store elements in a mapped fashion. Each element has a key value and a mapped value. No two mapped values can have the same key values. Maps are part of the C++ STL (Standard Template Library). Maps are the associative containers that store sorted key-value pair, in which each key is unique and it can be inserted or deleted but cannot be altered. Values associated with keys can be changed. The key values are good for sorting and identifying elements uniquely. The mapped values are for storing content associated with the key. The two may differ in types, but the member type combines them via a pair type that combines both.
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.
Strings are objects that represent sequences of characters. The standard string class provides support for such objects with an interface similar to that of a standard container of bytes, but adding features specifically designed to operate with strings of single-byte characters. The string class is an instantiation of the basic_string class template that uses char (i.e., bytes) as its character type, with its default char_traits and allocator types. Note that this class handles bytes independently of the encoding used: If used to handle sequences of multi-byte or variable-length characters (such as UTF-8), all members of this class (such as length or size), as well as its iterators, will still operate in terms of bytes (not actual encoded characters).
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.
#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.
Get iterator to element. Searches the container for an element with a key equivalent to k and returns an iterator to it if found, otherwise it returns an iterator to map::end. Two keys are considered equivalent if the container's comparison object returns false reflexively (i.e., no matter the order in which the elements are passed as arguments). Another member function, map::count, can be used to just check whether a particular key exists. The function accepts one mandatory parameter key which specifies the key to be searched in the map container.
Get characters. Extracts characters from the stream, as unformatted input. The get() function is used to read a character(at a time) from a file. The classes istream and ostream define two member functions get(), put() respectively to handle the single character input/output operations. There are two types of get() functions. Both get(char *) and get(void) prototype can be used to fetch a character including the blank space,tab and newline character. The get(char *) version assigns the input character to its argument and the get(void) version returns the input character. Since these functions are members of input/output Stream classes, these must be invoked using appropriate objects.
Iterators are just like pointers used to access the container elements. Iterators are one of the four pillars of the Standard Template Library or STL in C++. An iterator is used to point to the memory address of the STL container classes. For better understanding, you can relate them with a pointer, to some extent. Iterators act as a bridge that connects algorithms to STL containers and allows the modifications of the data present inside the container. They allow you to iterate over the container, access and assign the values, and run different operators over them, to get the desired result. • Iterators are used to traverse from one element to another element, a process is known as iterating through the container. • The main advantage of an iterator is to provide a common interface for all the containers type. • Iterators make the algorithm independent of the type of the container used.
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.
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.
The cin object is used to accept input from the standard input device i.e. keyboard. It is defined in the iostream header file. C++ cin statement is the instance of the class istream and is used to read input from the standard input device which is usually a keyboard. The extraction operator(>>) is used along with the object cin for reading inputs. The extraction operator extracts the data from the object cin which is entered using the keyboard. The "c" in cin refers to "character" and "in" means "input". Hence cin means "character input". The cin object is used along with the extraction operator >> in order to receive a stream of characters.
Return iterator to end. Returns an iterator referring to the past-the-end element in the map container. The past-the-end element is the theoretical element that would follow the last element in the map container. It does not point to any element, and thus shall not be dereferenced. Because the ranges used by functions of the standard library do not include the element pointed by their closing iterator, this function is often used in combination with map::begin to specify a range including all the elements in the container. If the container is empty, this function returns the same as map::begin.
Get type name. name() returns a null-terminated character sequence that may identify the type. The particular representation pointed by the returned value is implementation-defined, and may or may not be different for different types. This function does not accept any parameter.
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.
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.
In C++, pair is defined as a container in a header library <utility> which combines the two data elements having either the same data types or different data types. In general, the pair in C++ is defined as a tuple in Python programming language which also can give the output as a combined result of joining the two items specified by the pair container and it consists of the first element will be first and the second element will be second only it cannot be disturbed in the order or sequence of elements specified and are always accessed by the dot operator followed by the keyword "first" and "second" elements respectively. In C++ the pair is a container in <utility> header and is also a container class in STL (Standard Template Library) which uses "std" namespace so it will be as std::pair template class for demonstrating pair as a tuple.
Insert elements. Extends the container by inserting new elements, effectively increasing the container size by the number of elements inserted. Because element keys in a map are unique, the insertion operation checks whether each inserted element has a key equivalent to the one of an element already in the container, and if so, the element is not inserted, returning an iterator to this existing element (if the function returns a value). For a similar container allowing for duplicate elements, see multimap. An alternative way to insert elements in a map is by using member function map::operator[].
