C++ Programming Code Examples
C++ > Recursion Code Examples
Find GCD of Two Numbers Using Recursive Euclid Algorithm
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/* Find GCD of Two Numbers Using Recursive Euclid Algorithm
This is a C++ Program to find GCD of two numbers using Recursive Euclid Algorithm. In mathematics, the Euclidean algorithm, or Euclid's algorithm, is a method for computing the greatest common divisor (GCD) of two (usually positive) integers, also known as the greatest common factor (GCF) or highest common factor (HCF). It is named after the Greek mathematician Euclid, who described it in Books VII and X of his Elements.
The GCD of two positive integers is the largest integer that divides both of them without leaving a remainder (the GCD of two integers in general is defined in a more subtle way).
In its simplest form, Euclid's algorithm starts with a pair of positive integers, and forms a new pair that consists of the smaller number and the difference between the larger and smaller numbers. The process repeats until the numbers in the pair are equal. That number then is the greatest common divisor of the original pair of integers.
The main principle is that the GCD does not change if the smaller number is subtracted from the larger number. For example, the GCD of 252 and 105 is exactly the GCD of 147 (= 252 - 105) and 105. Since the larger of the two numbers is reduced, repeating this process gives successively smaller numbers, so this repetition will necessarily stop sooner or later - when the numbers are equal (if the process is attempted once more, one of the numbers will become 0). */
#include<iostream>
#include<conio.h>
#include<stdlib.h>
using namespace std;
int gcd(int u, int v)
{
return (v != 0) ? gcd(v, u % v) : u;
}
int main(void)
{
int number1, number2, result;
cout << "Enter two numbers to find GCD using Euclidean algorithm: ";
cin >> number1 >> number2;
result = gcd(number1, number2);
if (gcd)
cout << "\nThe GCD of " << number1 << " and " << number2 << " is: " << result
<< endl;
else
cout << "\nInvalid input!!!\n";
return 0;
}
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";
<<
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;
}
If Else Statement in C++
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,
Syntax for If Statement in C++
if (condition) {
// body of if statement
}
Syntax for If...Else Statement
if (condition) {
// block of code if condition is true
}
else {
// block of code if condition is false
}
Syntax for If...Else...Else If Statement in C++
if (condition1) {
// code block 1
}
else if (condition2){
// code block 2
}
else {
// code block 3
}
Syntax for If Else If Ladder in C++
if (condition)
statement 1;
else if (condition)
statement 2;
.
.
else
statement;
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/* If Else Statement in C++ Language */
#include <iostream>
using namespace std;
int main () {
// local variable declaration:
int a = 100;
// check the boolean condition
if( a < 20 ) {
// if condition is true then print the following
cout << "a is less than 20;" << endl;
} else {
// if condition is false then print the following
cout << "a is not less than 20;" << endl;
}
cout << "value of a is : " << a << endl;
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
}
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
}
}
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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;
}
Standard Input Stream (cin) in C++
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.
Syntax for Standard Input Stream (cin) in C++
cin >> var_name;
>>
is the extraction operator.
var_name
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.
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/* Standard Input Stream (cin) in C++ language */
// cin with Member Functions
#include <iostream>
using namespace std;
int main() {
char name[20], address[20];
cout << "Name: ";
// use cin with getline()
cin.getline(name, 20);
cout << "Address: ";
cin.getline(address, 20);
cout << endl << "You entered " << endl;
cout << "Name = " << name << endl;
cout << "Address = " << address;
return 0;
}
Return Statement in C++
A return statement ends the processing of the current function and returns control to the caller of the function. A value-returning function should include a return statement, containing an expression.
If an expression is not given on a return statement in a function declared with a non-void return type, the compiler issues an error message.
If the data type of the expression is different from the function return type, conversion of the return value takes place as if the value of the expression were assigned to an object with the same function return type.
Syntax for Return Statement in C++
return[expression];
return; /* Returns no value */
return result; /* Returns the value of result */
return 1; /* Returns the value 1 */
return (x * x); /* Returns the value of x * x */
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/* illustrate Methods returning a value using return statement in C++ code example */
#include <iostream>
using namespace std;
// non-void return type
// function to calculate sum
int SUM(int a, int b)
{
int s1 = a + b;
// method using the return
// statement to return a value
return s1;
}
// Driver method
int main()
{
int num1 = 10;
int num2 = 10;
int sum_of = SUM(num1, num2);
cout << "The sum is " << sum_of;
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;
}
Comments in C++
The C++ comments are statements that are not executed by the compiler. The comments in C++ programming can be used to provide explanation of the code, variable, method or class. If we write comments on our code, it will be easier for us to understand the code in the future. Also, it will be easier for your fellow developers to understand the code. By the help of comments, you can hide the program code also. There are two types of comments in C++:
• Single Line comment
• Multi Line comment
Syntax for Single Line Comment in C++
/* This is a comment */
Syntax for Multi Line Comment in C++
/* C++ comments can also
* span multiple lines
*/
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/* program to illustrate use comments in C++ language */
#include <ostream>
using namespace std;
int main()
{
int x = 11; // x is a variable
cout<<x<<"\n";
/* declare and
print variable in C++ */
int x = 35;
cout<<x<<"\n";
// This is a comment
cout << "Hello World!";
/* Multi-line Comments
in C++ */
}
#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"
#include <header_file>
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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;
}
Algorithm Library equal() Function in C++
Test whether the elements in two ranges are equal. Compares the elements in the range [first1,last1) with those in the range beginning at first2, and returns true if all of the elements in both ranges match.
C++ Algorithm equal()function compares the elements in both the containers and returns a true value if all the elements in both the containers are found to be matching. The first range is from [first1,last1) and the second starts from first2.
The elements are compared using operator== (or pred, in version (2)).
Syntax for Algorithm equal() Function in C++
#include <algorithm>
//equality (1)
template <class InputIterator1, class InputIterator2>
bool equal (InputIterator1 first1, InputIterator1 last1,
InputIterator2 first2);
//predicate (2)
template <class InputIterator1, class InputIterator2, class BinaryPredicate>
bool equal (InputIterator1 first1, InputIterator1 last1,
InputIterator2 first2, BinaryPredicate pred);
first1, last1
Input iterators to the initial and final positions of the first sequence. The range used is [first1,last1), which contains all the elements between first1 and last1, including the element pointed by first1 but not the element pointed by last1.
first2
Input iterator to the initial position of the second sequence. The comparison includes up to as many elements of this sequence as those in the range [first1,last1).
pred
Binary function that accepts two elements as argument (one of each of the two sequences, in the same order), and returns a value convertible to bool. The value returned indicates whether the elements are considered to match in the context of this function.
The function shall not modify any of its arguments.
This can either be a function pointer or a function object.
Function returns true if all the elements in the range [first1,last1) compare equal to those of the range starting at first2, and false otherwise.
Complexity
Up to linear in the distance between first1 and last1: Compares elements until a mismatch is found.
Data races
Some (or all) of the objects in both ranges are accessed (once at most).
Exceptions
Throws if any of the element comparisons (or pred) throws, or if any of the operations on iterators throws. Note that invalid parameters cause undefined behavior.
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/* The C++ function std::algorithm::equal() tests whether two sets of element are equal or not. Size of the both set need not to be equal. It uses binary predicate for comparison. */
/* compare the elements in both the containers and returns a true value if all the elements in both the containers are found to be matching by equal() function code example. */
#include <bits/stdc++.h>
bool pred(int i, int j)
{
return (i != j);
}
int main()
{
int v1[] = { 10, 20, 30, 40, 50 };
std::vector<int> vector_1 (v1, v1 + sizeof(v1) / sizeof(int) );
// Printing vector1
std::cout << "Vector contains : ";
for (unsigned int i = 0; i < vector_1.size(); i++)
std::cout << " " << vector_1[i];
std::cout << "\n";
// using std::equal()
// Comparison based on pred
if ( std::equal (vector_1.begin(), vector_1.end(), v1, pred) )
std::cout << "The contents of both sequences are equal.\n";
else
printf("The contents of both sequences differ.");
}
This is a C++ Program to check whether point lies above, below or on the line. For example, the equation of the line connecting points (2, 2) and (4, 5) is -3x + 2y + 2 = 0. The point (6, 3)
Using the bellman-ford algorithm to find the shortest path between two vertices assuming that negative size edges exist in the graph. A Program to find the 'shortest path' algorithm
To reverse a number in C++, then you have to ask to the user to enter a number. Now, start reversing that number to find its reverse and then display its reverse on the screen. Make a
To encrypt & decrypt file content in C++, you have to enter the file name with extension to encrypt & decrypt the content present inside the file. Now open that file using the function