C++ Programming Code Examples

#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. 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. 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.

In computer programming, loops are used to repeat a block of code. For example, when you are displaying number from 1 to 100 you may want set the value of a variable to 1 and display it 100 times, increasing its value by 1 on each loop iteration. When you know exactly how many times you want to loop through a block of code, use the for loop instead of a while loop. A for loop is a repetition control structure that allows you to efficiently write a loop that needs to execute a specific number of times. initializes variables and is executed only once. if true, the body of for loop is executed, if false, the for loop is terminated. updates the value of initialized variables and again checks the condition. A new range-based for loop was introduced to work with collections such as arrays and vectors.

In C++, classes and structs are blueprints that are used to create the instance of a class. Structs are used for lightweight objects such as Rectangle, color, Point, etc. Unlike class, structs in C++ are value type than reference type. It is useful if you have data that is not intended to be modified after creation of struct. C++ Structure is a collection of different data types. It is similar to the class that holds different types of data. A structure is declared by preceding the struct keyword followed by the identifier(structure name). Inside the curly braces, we can declare the member variables of different types. Consider the following situation: In the above case, Teacher is a structure contains three variables name, id, and age. When the structure is declared, no memory is allocated. When the variable of a structure is created, then the memory is allocated. Let's understand this scenario. Structures in C++ can contain two types of members: • Data Member: These members are normal C++ variables. We can create a structure with variables of different data types in C++. • Member Functions: These members are normal C++ functions. Along with variables, we can also include functions inside a structure declaration. Structure variable can be defined as: Teacher s; Here, s is a structure variable of type Teacher. When the structure variable is created, the memory will be allocated. Teacher structure contains one char variable and two integer variable. Therefore, the memory for one char variable is 1 byte and two ints will be 2*4 = 8. The total memory occupied by the s variable is 9 byte. The variable of the structure can be accessed by simply using the instance of the structure followed by the dot (.) operator and then the field of the structure. We are accessing the id field of the structure Teacher by using the dot(.) operator and assigns the value 4 to the id field. In C++, the struct keyword is optional before in declaration of a variable. In C, it is mandatory.

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. is the extraction operator. is usually a variable, but can also be an element of containers like arrays, vectors, lists, etc. 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. The >> operator can also be used more than once in the same statement to accept multiple inputs. The cin object can also be used with other member functions such as getline(), read(), etc. Some of the commonly used member functions are: • cin.get(char &ch): Reads an input character and stores it in ch. • cin.getline(char *buffer, int length): Reads a stream of characters into the string buffer, It stops when: it has read length-1 characters or when it finds an end-of-line character '\n' or the end of the file eof. • cin.read(char *buffer, int n): Reads n bytes (or until the end of the file) from the stream into the buffer. • cin.ignore(int n): Ignores the next n characters from the input stream. • cin.eof(): Returns a non-zero value if the end of file (eof) is reached. The prototype of cin as defined in the iostream header file is: extern istream cin; The cin object in C++ is an object of class istream. It is associated with the standard C input stream stdin. The cin object is ensured to be initialized during or before the first time an object of type ios_base::Init is constructed. After the cin object is constructed, cin.tie() returns &cout. This means that any formatted input operation on cin forces a call to cout.flush() if any characters are pending for output.

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. 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 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.

An array is defined as the collection of similar type of data items stored at contiguous memory locations. Arrays are the derived data type in C++ programming language which can store the primitive type of data such as int, char, double, float, etc. It also has the capability to store the collection of derived data types, such as pointers, structure, etc. The array is the simplest data structure where each data element can be randomly accessed by using its index number. C++ array is beneficial if you have to store similar elements. For example, if we want to store the marks of a student in 6 subjects, then we don't need to define different variables for the marks in the different subject. Instead of that, we can define an array which can store the marks in each subject at the contiguous memory locations. By using the array, we can access the elements easily. Only a few lines of code are required to access the elements of the array. The array contains the following properties. • Each element of an array is of same data type and carries the same size, i.e., int = 4 bytes. • Elements of the array are stored at contiguous memory locations where the first element is stored at the smallest memory location. • Elements of the array can be randomly accessed since we can calculate the address of each element of the array with the given base address and the size of the data element. • 1) Code Optimization: Less code to the access the data. • 2) Ease of traversing: By using the for loop, we can retrieve the elements of an array easily. • 3) Ease of sorting: To sort the elements of the array, we need a few lines of code only. • 4) Random Access: We can access any element randomly using the array. • 1) Allows a fixed number of elements to be entered which is decided at the time of declaration. Unlike a linked list, an array in C++ is not dynamic. • 2) Insertion and deletion of elements can be costly since the elements are needed to be managed in accordance with the new memory allocation. To declare an array in C++, a programmer specifies the type of the elements and the number of elements required by an array as follows This is called a single-dimensional array. The arraySize must be an integer constant greater than zero and type can be any valid C++ data type. For example, to declare a 10-element array called balance of type double, use this statement Here balance is a variable array which is sufficient to hold up to 10 double numbers. You can initialize an array in C++ either one by one or using a single statement as follows The number of values between braces { } cannot be larger than the number of elements that we declare for the array between square brackets [ ]. If you omit the size of the array, an array just big enough to hold the initialization is created. Therefore, if you write An element is accessed by indexing the array name. This is done by placing the index of the element within square brackets after the name of the array. The above statement will take the 10^th element from the array and assign the value to salary variable.

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. Function returns a pointer to a c-string with the name for the object. This member function never throws exceptions.

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. A namespace definition begins with the keyword namespace followed by the namespace name as follows: To call the namespace-enabled version of either function or variable, prepend (::) the namespace name as follows: 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. 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: Namespaces can be nested where you can define one namespace inside another name space as follows: • 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.