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C++ Programming Code Examples

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Print the maximum number of pairs that DateMap can hold

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/* Print the maximum number of pairs that DateMap can hold */ #include <map> #include <iostream> #include <string> using namespace std; typedef map<string, int> STRING2INT; int main(void) { STRING2INT DateMap; STRING2INT::iterator DateIterator; string DateBuffer; cout << "DateMap is capable of holding " << DateMap.max_size() << " <string,int> pairs" << endl; }
Standard Output Stream (cout) in C++
The cout is a predefined object of ostream class. It is connected with the standard output device, which is usually a display screen. The cout is used in conjunction with stream insertion operator (<<) to display the output on a console. On most program environments, the standard output by default is the screen, and the C++ stream object defined to access it is cout.
Syntax for cout in C++
cout << var_name; //or cout << "Some String";
The syntax of the cout object in C++: cout << var_name; Or cout << "Some String";
<<
is the insertion operator
var_name
is usually a variable, but can also be an array element or elements of containers like vectors, lists, maps, etc. The "c" in cout refers to "character" and "out" means "output". Hence cout means "character output". The cout object is used along with the insertion operator << in order to display a stream of characters. The << operator can be used more than once with a combination of variables, strings, and manipulators. cout is used for displaying data on the screen. The operator << called as insertion operator or put to operator. The Insertion operator can be overloaded. Insertion operator is similar to the printf() operation in C. cout is the object of ostream class. Data flow direction is from variable to output device. Multiple outputs can be displayed using cout.
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/* standard output stream (cout) in C++ language */ #include <iostream> using namespace std; int main() { string str = "Do not interrupt me"; char ch = 'm'; // use cout with write() cout.write(str,6); cout << endl; // use cout with put() cout.put(ch); return 0; }
main() Function in C++
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.
Syntax for main() Function in C++
void main() { ............ ............ }
void
void is a keyword in C++ language, void means nothing, whenever we use void as a function return type then that function nothing return. here main() function no return any value.
main
main is a name of function which is predefined function in C++ library. In place of void we can also use int return type of main() function, at that time main() return integer type value. 1) It cannot be used anywhere in the program a) in particular, it cannot be called recursively b) its address cannot be taken 2) It cannot be predefined and cannot be overloaded: effectively, the name main in the global namespace is reserved for functions (although it can be used to name classes, namespaces, enumerations, and any entity in a non-global namespace, except that a function called "main" cannot be declared with C language linkage in any namespace). 3) It cannot be defined as deleted or (since C++11) declared with C language linkage, constexpr (since C++11), consteval (since C++20), inline, or static. 4) The body of the main function does not need to contain the return statement: if control reaches the end of main without encountering a return statement, the effect is that of executing return 0;. 5) Execution of the return (or the implicit return upon reaching the end of main) is equivalent to first leaving the function normally (which destroys the objects with automatic storage duration) and then calling std::exit with the same argument as the argument of the return. (std::exit then destroys static objects and terminates the program). 6) (since C++14) The return type of the main function cannot be deduced (auto main() {... is not allowed). 7) (since C++20) The main function cannot be a coroutine.
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/* simple code example by main() function in C++ */ #include <iostream> using namespace std; int main() { int day = 4; switch (day) { case 1: cout << "Monday"; break; case 2: cout << "Tuesday"; break; case 3: cout << "Wednesday"; break; case 4: cout << "Thursday"; break; case 5: cout << "Friday"; break; case 6: cout << "Saturday"; break; case 7: cout << "Sunday"; break; } return 0; }
#include Directive in C++
#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.
Syntax for #include Directive in C++
#include "user-defined_file"
Including using " ": When using the double quotes(" "), the preprocessor access the current directory in which the source "header_file" is located. This type is mainly used to access any header files of the user's program or user-defined files.
#include <header_file>
Including using <>: While importing file using angular brackets(<>), the the preprocessor uses a predetermined directory path to access the file. It is mainly used to access system header files located in the standard system directories. Header File or Standard files: This is a file which contains C/C++ function declarations and macro definitions to be shared between several source files. Functions like the printf(), scanf(), cout, cin and various other input-output or other standard functions are contained within different header files. So to utilise those functions, the users need to import a few header files which define the required functions. User-defined files: These files resembles the header files, except for the fact that they are written and defined by the user itself. This saves the user from writing a particular function multiple times. Once a user-defined file is written, it can be imported anywhere in the program using the #include preprocessor. • In #include directive, comments are not recognized. So in case of #include <a//b>, a//b is treated as filename. • In #include directive, backslash is considered as normal text not escape sequence. So in case of #include <a\nb>, a\nb is treated as filename. • You can use only comment after filename otherwise it will give error.
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/* using #include directive in C language */ #include <stdio.h> int main() { /* * C standard library printf function * defined in the stdio.h header file */ printf("I love you Clementine"); printf("I love you so much"); printf("HappyCodings"); return 0; }
Namespaces in C++ Language
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. A namespace is designed to overcome this difficulty and is used as additional information to differentiate similar functions, classes, variables etc. with the same name available in different libraries. Using namespace, you can define the context in which names are defined. In essence, a namespace defines a scope.
Defining a Namespace
A namespace definition begins with the keyword namespace followed by the namespace name as follows:
namespace namespace_name { // code declarations }
To call the namespace-enabled version of either function or variable, prepend (::) the namespace name as follows:
name::code; // code could be variable or function.
Using Directive
You can also avoid prepending of namespaces with the using namespace directive. This directive tells the compiler that the subsequent code is making use of names in the specified namespace.
Discontiguous Namespaces
A namespace can be defined in several parts and so a namespace is made up of the sum of its separately defined parts. The separate parts of a namespace can be spread over multiple files. So, if one part of the namespace requires a name defined in another file, that name must still be declared. Writing a following namespace definition either defines a new namespace or adds new elements to an existing one:
namespace namespace_name { // code declarations }
Nested Namespaces
Namespaces can be nested where you can define one namespace inside another name space as follows:
namespace namespace_name1 { // code declarations namespace namespace_name2 { // code declarations } }
• Namespace is a feature added in C++ and not present in C. • A namespace is a declarative region that provides a scope to the identifiers (names of the types, function, variables etc) inside it. • Multiple namespace blocks with the same name are allowed. All declarations within those blocks are declared in the named scope. • Namespace declarations appear only at global scope. • Namespace declarations can be nested within another namespace. • Namespace declarations don't have access specifiers. (Public or private) • No need to give semicolon after the closing brace of definition of namespace. • We can split the definition of namespace over several units.
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/* namespaces in C++ language */ // A C++ code to demonstrate that we can define // methods outside namespace. #include <iostream> using namespace std; // Creating a namespace namespace ns { void display(); class happy { public: void display(); }; } // Defining methods of namespace void ns::happy::display() { cout << "ns::happy::display()\n"; } void ns::display() { cout << "ns::display()\n"; } // Driver code int main() { ns::happy obj; ns::display(); obj.display(); return 0; }
Map Library max_size() Function in C++
Return maximum size. Returns the maximum number of elements that the map container can hold. The map::max_size() is a built-in function in C++ STL which returns the maximum number of elements a map container can hold. This is the maximum potential size the container can reach due to known system or library implementation limitations, but the container is by no means guaranteed to be able to reach that size: it can still fail to allocate storage at any point before that size is reached.
Syntax for Map max_size() Function in C++
#include <map> size_type max_size() const noexcept;
No parameter is required. Function returns the maximum number of elements a map container can hold as content. Member type size_type is an unsigned integral type.
Complexity
Constant
Iterator validity
No changes
Data races
The container is accessed. No elements are accessed: concurrently accessing or modifying them is safe.
Exception safety
No-throw guarantee: this member function never throws exceptions.
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/* map::max_size() function is an inbuilt function in C++ STL, which is defined in <map> header file. max_size() is used to return the maximum size of the map container. This function is used to check the maximum number of values that a map container can hold. The size is like the potential of the container, hence there is no guarantee that it can reach that value or not. */ /* get the maximum size a map container can hold by map max_size() function code example. */ #include <iostream> #include <map> using namespace std; int main (){ map<int, string> MyMap; map<int, string>::iterator it; MyMap[101] = "John"; MyMap[102] = "Marry"; MyMap[103] = "Kim"; MyMap[104] = "Jo"; MyMap[105] = "Ramesh"; cout<<"The map contains:\n"; for(it = MyMap.begin(); it != MyMap.end(); ++it) cout<<it->first<<" "<<it->second<<"\n"; cout<<"\nMap size is: "<<MyMap.size()<<"\n"; cout<<"Maximum size of the Map: "<<MyMap.max_size()<<"\n"; return 0; }
Iterators in C++ Language
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.
Syntax for Iterators in C++
<ContainerType> :: iterator; <ContainerType> :: const_iterator;
• 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. • Iterators provide a generic approach to navigate through the elements of a container. Operator (*) : The '*' operator returns the element of the current position pointed by the iterator. Operator (++) : The '++' operator increments the iterator by one. Therefore, an iterator points to the next element of the container. Operator (==) and Operator (!=) : Both these operators determine whether the two iterators point to the same position or not. Operator (=) : The '=' operator assigns the iterator. Iterators can be smart pointers which allow to iterate over the complex data structures. A Container provides its iterator type. Therefore, we can say that the iterators have the common interface with different container type. The container classes provide two basic member functions that allow to iterate or move through the elements of a container: begin(): The begin() function returns an iterator pointing to the first element of the container. end(): The end() function returns an iterator pointing to the past-the-last element of the container. Input Iterator: An input iterator is an iterator used to access the elements from the container, but it does not modify the value of a container. Operators used for an input iterator are: Increment operator(++), Equal operator(==), Not equal operator(!=), Dereference operator(*). Output Iterator: An output iterator is an iterator used to modify the value of a container, but it does not read the value from a container. Therefore, we can say that an output iterator is a write-only iterator. Operators used for an output iterator are: Increment operator(++), Assignment operator(=). Forward Iterator: A forward iterator is an iterator used to read and write to a container. It is a multi-pass iterator. Operators used for a Forward iterator are: Increment operator(++), Assignment operator(=), Equal operator(=), Not equal operator(!=). Bidirectional iterator: A bidirectional iterator is an iterator supports all the features of a forward iterator plus it adds one more feature, i.e., decrement operator(--). We can move backward by decrementing an iterator. Operators used for a Bidirectional iterator are: Increment operator(++), Assignment operator(=), Equal operator(=), Not equal operator(!=), Decrement operator(--). Random Access Iterator: A Random Access iterator is an iterator provides random access of an element at an arbitrary location. It has all the features of a bidirectional iterator plus it adds one more feature, i.e., pointer addition and pointer subtraction to provide random access to an element. Following are the disadvantages of an iterator: • If we want to move from one data structure to another at the same time, iterators won't work. • If we want to update the structure which is being iterated, an iterator won?t allow us to do because of the way it stores the position. • If we want to backtrack while processing through a list, the iterator will not work in this case. Following are the advantages of an iterator: • Ease in programming: It is convenient to use iterators rather than using a subscript operator[] to access the elements of a container. If we use subscript operator[] to access the elements, then we need to keep the track of the number of elements added at the runtime, but this would not happen in the case of an iterator. • Code Reusability: A code can be reused if we use iterators. In the above example, if we replace vector with the list, and then the subscript operator[] would not work to access the elements as the list does not support the random access. However, we use iterators to access the elements, then we can also access the list elements. • Dynamic Processing: C++ iterators provide the facility to add or delete the data dynamically.
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/* Iterators in C++ language */ // C++ code to demonstrate the working of next() and prev() #include<iostream> #include<iterator> // for iterators #include<vector> // for vectors using namespace std; int main() { vector<int> ar = { 1, 2, 3, 4, 5 }; // Declaring iterators to a vector vector<int>::iterator ptr = ar.begin(); vector<int>::iterator ftr = ar.end(); // Using next() to return new iterator // points to 4 auto it = next(ptr, 3); // Using prev() to return new iterator // points to 3 auto it1 = prev(ftr, 3); // Displaying iterator position cout << "The position of new iterator using next() is : "; cout << *it << " "; cout << endl; // Displaying iterator position cout << "The position of new iterator using prev() is : "; cout << *it1 << " "; cout << endl; return 0; }
Maps in C++ Language
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.
Syntax for Map in C++
template < class Key, // map::key_type class T, // map::mapped_type class Compare = less<Key>, // map::key_compare class Alloc = allocator<pair<const Key,T> > // map::allocator_type > class map;
key
The key data type to be stored in the map.
type
The data type of value to be stored in the map.
compare
A comparison class that takes two arguments of the same type bool and returns a value. This argument is optional and the binary predicate less<"key"> is the default value.
alloc
Type of the allocator object. This argument is optional and the default value is allocator. Maps can easily be created using the following statement:
typedef pair<const Key, T> value_type;
The above form will use to create a map with key of type Key type and value of type value type. One important thing is that key of a map and corresponding values are always inserted as a pair, you cannot insert only key or just a value in a map. • begin: Returns an iterator pointing to the first element in the map. • cbegin: Returns a const iterator pointing to the first element in the map. • end: Returns an iterator pointing to the past-end. • cend: Returns a constant iterator pointing to the past-end. • rbegin: Returns a reverse iterator pointing to the end. • rend: Returns a reverse iterator pointing to the beginning. • crbegin: Returns a constant reverse iterator pointing to the end. • crend: Returns a constant reverse iterator pointing to the beginning. • empty: Returns true if map is empty. • size: Returns the number of elements in the map. • max_size: Returns the maximum size of the map. • operator[]: Retrieve the element with given key. • at: Retrieve the element with given key. • insert: Insert element in the map. • erase: Erase elements from the map. • swap: Exchange the content of the map. • clear: Delete all the elements of the map. • emplace: Construct and insert the new elements into the map. • emplace_hint: Construct and insert new elements into the map by hint. • key_comp: Return a copy of key comparison object. • value_comp: Return a copy of value comparison object. • find: Search for an element with given key. • count: Gets the number of elements matching with given key. • lower_bound: Returns an iterator to lower bound. • upper_bound: Returns an iterator to upper bound. • equal_range: Returns the range of elements matches with given key. • get_allocator Returns an allocator object that is used to construct the map. • operator==: Checks whether the two maps are equal or not. • operator!=: Checks whether the two maps are equal or not. • operator<: Checks whether the first map is less than other or not. • operator<=: Checks whether the first map is less than or equal to other or not. • operator>: Checks whether the first map is greater than other or not. • operator>=: Checks whether the first map is greater than equal to other or not. • swap(): Exchanges the element of two maps.
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/* how to implement maps in C++ language*/ #include <iostream> #include <iterator> #include <map> using namespace std; int main() { map<int, int> marks; marks.insert(pair<int, int>(160, 42)); marks.insert(pair<int, int>(161, 30)); marks.insert(pair<int, int>(162, 40)); marks.insert(pair<int, int>(163, 50)); marks.insert(pair<int, int>(164, 31)); marks.insert(pair<int, int>(165, 12)); marks.insert(pair<int, int>(166, 34)); map<int, int>::iterator itr; cout << "nThe map marks is : n"; cout << "ROLL NO.tMarksn"; for (itr = marks.begin(); itr != marks.end(); ++itr) { cout << itr->first << "t t" << itr->second << 'n'; } cout << endl; int num; num = marks.erase(164); cout << "nmarks.erase(164) : "; cout << num << " removed n"; cout << "tROLL NO. tMarksn"; for (itr = marks.begin(); itr != marks.end(); ++itr) { cout << 't' << itr->first << 't' << itr->second << 'n'; } return 0; }


Bubble sort algorithm sort data by comparing 2 consecutive numbers. The time Complexity of this algorithm is O(n^2). And compare two consecutive number. Switch values if number
In case of 'an array' we check that a given key or a number is present in array at any index or not by "comparing each element" of array. By traversing the whole data structure elements