C++ Programming Code Examples
C++ > Beginners Lab Assignments Code Examples
C++ Program to Implement Vector in STL
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/* C++ Program to Implement Vector in STL */
#include <iostream>
#include <vector>
#include <string>
#include <cstdlib>
using namespace std;
int main()
{
vector<int> ss;
vector<int>::iterator it;
int choice, item;
while (1)
{
cout<<"\n---------------------"<<endl;
cout<<"Vector Implementation in Stl"<<endl;
cout<<"\n---------------------"<<endl;
cout<<"1.Insert Element into the Vector"<<endl;
cout<<"2.Delete Last Element of the Vector"<<endl;
cout<<"3.Size of the Vector"<<endl;
cout<<"4.Display by Index"<<endl;
cout<<"5.Dislplay by Iterator"<<endl;
cout<<"6.Clear the Vector"<<endl;
cout<<"7.Exit"<<endl;
cout<<"Enter your Choice: ";
cin>>choice;
switch(choice)
{
case 1:
cout<<"Enter value to be inserted: ";
cin>>item;
ss.push_back(item);
break;
case 2:
cout<<"Delete Last Element Inserted:"<<endl;
ss.pop_back();
break;
case 3:
cout<<"Size of Vector: ";
cout<<ss.size()<<endl;
break;
case 4:
cout<<"Displaying Vector by Index: ";
for (int i = 0; i < ss.size(); i++)
{
cout<<ss[i]<<" ";
}
cout<<endl;
break;
case 5:
cout<<"Displaying Vector by Iterator: ";
for (it = ss.begin(); it != ss.end(); it++)
{
cout<<*it<<" ";
}
cout<<endl;
break;
case 6:
ss.clear();
cout<<"Vector Cleared"<<endl;
break;
case 7:
exit(1);
break;
default:
cout<<"Wrong Choice"<<endl;
}
}
return 0;
}
Vector Library begin() Function in C++
Return iterator to beginning. Returns an iterator pointing to the first element in the vector. Notice that, unlike member vector::front, which returns a reference to the first element, this function returns a random access iterator pointing to it.
If the container is empty, the returned iterator value shall not be dereferenced.
The C++ function std::vector::begin() returns a random access iterator pointing to the first element of the vector.
Syntax for Vector begin() Function in C++
#include <vector>
iterator begin() noexcept;
const_iterator begin() const noexcept;
Complexity
Constant
Iterator validity
No changes
Data races
The container is accessed (neither the const nor the non-const versions modify the container). No contained elements are accessed by the call, but the iterator returned can be used to access or modify elements. Concurrently accessing or modifying different elements is safe.
Exception safety
No-throw guarantee: this member function never throws exceptions. The copy construction or assignment of the returned iterator is also guaranteed to never throw.
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/* returns a random access iterator pointing to the first element of the vector by std::vector::begin() function code example. */
// CPP program to illustrate implementation of begin() function
#include <iostream>
#include <string>
#include <vector>
using namespace std;
int main()
{
// declaration of vector container
vector<string> myvector{ "This", "is",
"HappyCodings" };
// using begin() to print vector
for (auto it = myvector.begin();
it != myvector.end(); ++it)
cout << ' ' << *it;
return 0;
}
While Loop Statement in C++
In while loop, condition is evaluated first and if it returns true then the statements inside while loop execute, this happens repeatedly until the condition returns false. When condition returns false, the control comes out of loop and jumps to the next statement in the program after while loop.
The important point to note when using while loop is that we need to use increment or decrement statement inside while loop so that the loop variable gets changed on each iteration, and at some point condition returns false. This way we can end the execution of while loop otherwise the loop would execute indefinitely. A while loop that never stops is said to be the infinite while loop, when we give the condition in such a way so that it never returns false, then the loops becomes infinite and repeats itself indefinitely.
Syntax for While Loop Statement in C++
while (condition) {
// body of the loop
}
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/* While Loop Statement in C++ language */
// program to find the sum of positive numbers
// if the user enters a negative number, the loop ends
// the negative number entered is not added to the sum
#include <iostream>
using namespace std;
int main() {
int number;
int sum = 0;
// take input from the user
cout << "Enter a number: ";
cin >> number;
while (number >= 0) {
// add all positive numbers
sum += number;
// take input again if the number is positive
cout << "Enter a number: ";
cin >> number;
}
// display the sum
cout << "\nThe sum is " << sum << endl;
return 0;
}
Vector Library end() Function in C++
Return iterator to end. Returns an iterator referring to the past-the-end element in the vector container. The past-the-end element is the theoretical element that would follow the last element in the vector. 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 vector::begin to specify a range including all the elements in the container. If the container is empty, this function returns the same as vector::begin.
Syntax for Vector end() Function in C++
#include <vector>
iterator end() noexcept;
const_iterator end() const noexcept;
Complexity
Constant
Iterator validity
No changes
Data races
The container is accessed (neither the const nor the non-const versions modify the container). No contained elements are accessed by the call, but the iterator returned can be used to access or modify elements. Concurrently accessing or modifying different elements is safe.
Exception safety
No-throw guarantee: this member function never throws exceptions. The copy construction or assignment of the returned iterator is also guaranteed to never throw.
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/* returns the iterator pointing to the past-the-last element of the vector container by vector::end function code example. */
// CPP program to illustrate implementation of begin() function
#include <iostream>
#include <string>
#include <vector>
using namespace std;
int main()
{
// declaration of vector container
vector<string> myvector{ "This", "is",
"HappyCodings" };
// using begin() to print vector
for (auto it = myvector.begin();
it != myvector.end(); ++it)
cout << ' ' << *it;
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;
}
exit() Function in C++
The exit function terminates the program normally. Automatic objects are not destroyed, but static objects are. Then, all functions registered with atexit are called in the opposite order of registration. The code is returned to the operating system. An exit code of 0 or EXIT_SUCCESS means successful completion. If code is EXIT_FAILURE, an indication of program failure is returned to the operating system. Other values of code are implementation-defined.
Syntax for exit() Function in C++
void exit (int status);
status
Status code. If this is 0 or EXIT_SUCCESS, it indicates success. If it is EXIT_FAILURE, it indicates failure.
Calls all functions registered with the atexit() function, and destroys C++ objects with static storage duration, all in last-in-first-out (LIFO) order. C++ objects with static storage duration are destroyed in the reverse order of the completion of their constructor. (Automatic objects are not destroyed as a result of calling exit().)
Functions registered with atexit() are called in the reverse order of their registration. A function registered with atexit(), before an object obj1 of static storage duration is initialized, will not be called until obj1's destruction has completed. A function registered with atexit(), after an object obj2 of static storage duration is initialized, will be called before obj2's destruction starts.
Normal program termination performs the following (in the same order):
• Objects associated with the current thread with thread storage duration are destroyed (C++11 only).
• Objects with static storage duration are destroyed (C++) and functions registered with atexit are called.
• All C streams (open with functions in <cstdio>) are closed (and flushed, if buffered), and all files created with tmpfile are removed.
• Control is returned to the host environment.
Note that objects with automatic storage are not destroyed by calling exit (C++).
If status is zero or EXIT_SUCCESS, a successful termination status is returned to the host environment.
If status is EXIT_FAILURE, an unsuccessful termination status is returned to the host environment.
Otherwise, the status returned depends on the system and library implementation.
Flushes all buffers, and closes all open files.
All files opened with tmpfile() are deleted.
Returns control to the host environment from the program.
exit() returns no values.
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/* terminate the process normally, performing the regular cleanup for terminating programs by exit() function code example */
#include<iostream>
using namespace std;
int main()
{
int i;
cout<<"Enter a non-zero value: "; //user input
cin>>i;
if(i) // checks whether the user input is non-zero or not
{
cout<<"Valid input.\n";
}
else
{
cout<<"ERROR!"; //the program exists if the value is 0
exit(0);
}
cout<<"The input was : "<<i;
}
#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;
}
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;
}
Switch Case Statement in C++
Switch statement in C tests the value of a variable and compares it with multiple cases. Once the case match is found, a block of statements associated with that particular case is executed.
Each case in a block of a switch has a different name/number which is referred to as an identifier. The value provided by the user is compared with all the cases inside the switch block until the match is found.
If a case match is NOT found, then the default statement is executed, and the control goes out of the switch block.
Syntax for Switch Case Statement in C++
switch( expression )
{
case value-1:
Block-1;
Break;
case value-2:
Block-2;
Break;
case value-n:
Block-n;
Break;
default:
Block-1;
Break;
}
Statement-x;
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/* the switch statement helps in testing the equality of a variable against a set of values */
#include <iostream>
using namespace std;
int main () {
// local variable declaration:
char grade = 'D';
switch(grade) {
case 'A' :
cout << "Excellent!" << endl;
break;
case 'B' :
case 'C' :
cout << "Well done" << endl;
break;
case 'D' :
cout << "You passed" << endl;
break;
case 'F' :
cout << "Better try again" << endl;
break;
default :
cout << "Invalid grade" << endl;
}
cout << "Your grade is " << grade << endl;
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;
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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;
}
Vector Library Operator Index [] in C++
Access element. Returns a reference to the element at position n in the vector container.
A similar member function, vector::at, has the same behavior as this operator function, except that vector::at is bound-checked and signals if the requested position is out of range by throwing an out_of_range exception.
Portable programs should never call this function with an argument n that is out of range, since this causes undefined behavior.
Syntax for Vector Operator Index [] in C++
#include <vector>
reference operator[] (size_type n);
const_reference operator[] (size_type n) const;
n
Position of an element in the container. Notice that the first element has a position of 0 (not 1). Member type size_type is an unsigned integral type.
Function returns the element at the specified position in the vector.
If the vector object is const-qualified, the function returns a const_reference. Otherwise, it returns a reference.
Member types reference and const_reference are the reference types to the elements of the container (see vector member types).
Complexity
Constant
Iterator validity
No changes
Data races
The container is accessed (neither the const nor the non-const versions modify the container). The reference returned can be used to access or modify elements. Concurrently accessing or modifying different elements is safe.
Exception safety
If the container size is greater than n, the function never throws exceptions (no-throw guarantee). Otherwise, the behavior is undefined.
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/* Returns a reference to the element at specified location pos. No bounds checking is performed. Unlike std::map::operator[], this operator never inserts a new element into the container. Accessing a nonexistent element through this operator is undefined behavior. */
/* Access element from a vector by vector::operator[] code example */
#include <iostream>
#include <vector>
int main ()
{
std::vector<int> myvector (10); // 10 zero-initialized elements
std::vector<int>::size_type sz = myvector.size();
// assign some values:
for (unsigned i=0; i<sz; i++) myvector[i]=i;
// reverse vector using operator[]:
for (unsigned i=0; i<sz/2; i++)
{
int temp;
temp = myvector[sz-1-i];
myvector[sz-1-i]=myvector[i];
myvector[i]=temp;
}
std::cout << "myvector contains:";
for (unsigned i=0; i<sz; i++)
std::cout << ' ' << myvector[i];
std::cout << '\n';
return 0;
}
Vector Library push_back() Function in C++
Add element at the end. Adds a new element at the end of the vector, 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, which causes an automatic reallocation of the allocated storage space if -and only if- the new vector size surpasses the current vector capacity.
push_back() function is used to push elements into a vector from the back. The new value is inserted into the vector at the end, after the current last element and the container size is increased by 1.
Syntax for Vector push_back() Function in C++
#include <vector>
void push_back (const value_type& val);
void push_back (value_type&& val);
val
Value to be copied (or moved) to the new element. Member type value_type is the type of the elements in the container, defined in vector as an alias of its first template parameter (T).
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).
Complexity
Constant (amortized time, reallocation may happen). If a reallocation happens, the reallocation is itself up to linear in the entire size.
Iterator validity
If a reallocation happens, all iterators, pointers and references related to the container are invalidated.
Otherwise, only the end iterator is invalidated, and all iterators, pointers and references to elements are guaranteed to keep referring to the same elements they were referring to before the call.
Data races
The container is modified. If a reallocation happens, all contained elements are modified.
Otherwise, no existing element is accessed, and concurrently accessing or modifying them is safe.
Exception safety
If no reallocations happen, there are no changes in the container in case of exception (strong guarantee).
If a reallocation happens, the strong guarantee is also given if the type of the elements is either copyable or no-throw moveable.
Otherwise, the container is guaranteed to end in a valid state (basic guarantee).
If allocator_traits::construct is not supported with val as argument, it causes undefined behavior.
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/* vector::push_back() is a library function of "vector" header, it is used to insert/add an element at the end of the vector, it accepts an element of the same type and adds the given element at the end of the vector and increases the size of the vector. */
//C++ STL program code example to demonstrate example of vector::push_back() function
#include <iostream>
#include <vector>
using namespace std;
int main()
{
//vector declaration
vector<int> v1;
//inserting elements and printing size
cout << "size of v1: " << v1.size() << endl;
v1.push_back(10);
cout << "size of v1: " << v1.size() << endl;
v1.push_back(20);
v1.push_back(30);
v1.push_back(40);
v1.push_back(50);
cout << "size of v1: " << v1.size() << endl;
//printing all elements
cout << "elements of vector v1..." << endl;
for (int x : v1)
cout << x << " ";
cout << endl;
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;
}
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;
}
Vector Library clear() Function in C++
The C++ vector has many member functions. Two of them are clear() and erase(). clear() "removes" all the elements of the vector. erase() "removes" a single element or a range of elements. vector::clear() is a library function of "vector" header, it is used to remove/clear all elements of the vector, it makes the 0 sized vector after removing all elements.
The C++ vector::clear function is used to clear all elements of the vector. This function makes the vector empty with a size of zero.
Syntax for Vector clear() Function in C++
#include <vector>
void clear() noexcept;
Complexity
Linear in size (destructions). This may be optimized to constant complexity for trivially-destructible types (such as scalar or PODs), where elements need not be destroyed.
Iterator validity
All iterators, pointers and references related to this container are invalidated.
Data races
The container is modified. All contained elements are modified.
Exception safety
No-throw guarantee: this member function never throws exceptions.
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/* clear all elements of the vector by vector::clear function code example */
#include <iostream>
#include <vector>
using namespace std;
int main (){
vector<int> MyVector{10, 20, 30, 40, 50};
vector<int>::iterator it;
cout<<"Before clear() function: \nMyVector contains:";
for(it = MyVector.begin(); it != MyVector.end(); ++it)
cout<<" "<<*it;
cout<<"\nMyVector size is: "<<MyVector.size()<<"\n\n";
MyVector.clear();
cout<<"After clear() function: \nMyVector contains:";
for(it = MyVector.begin(); it != MyVector.end(); ++it)
cout<<" "<<*it;
cout<<"\nMyVector size is: "<<MyVector.size();
return 0;
}
For Loop Statement in C++
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.
Syntax of For Loop Statement in C++
for (initialization; condition; update) {
// body of-loop
}
initialization
initializes variables and is executed only once.
condition
if true, the body of for loop is executed, if false, the for loop is terminated.
update
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.
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/* For Loop Statement in C++ Language */
// C++ program to find the sum of first n natural numbers
// positive integers such as 1,2,3,...n are known as natural numbers
#include <iostream>
using namespace std;
int main() {
int num, sum;
sum = 0;
cout << "Enter a positive integer: ";
cin >> num;
for (int i = 1; i <= num; ++i) {
sum += i;
}
cout << "Sum = " << sum << endl;
return 0;
}
Break Statement in C++
Break statement in C++ is a loop control statement defined using the break keyword. It is used to stop the current execution and proceed with the next one. When a compiler calls the break statement, it immediately stops the execution of the loop and transfers the control outside the loop and executes the other statements. In the case of a nested loop, break the statement stops the execution of the inner loop and proceeds with the outer loop. The statement itself says it breaks the loop. When the break statement is called in the program, it immediately terminates the loop and transfers the flow control to the statement mentioned outside the loop.
Syntax for Break Statement in C++
// jump-statement;
break;
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/* break statement with while loop code example */
// program to find the sum of positive numbers
// if the user enters a negative numbers, break ends the loop
// the negative number entered is not added to sum
#include <iostream>
using namespace std;
int main() {
int number;
int sum = 0;
while (true) {
// take input from the user
cout << "Enter a number: ";
cin >> number;
// break condition
if (number < 0) {
break;
}
// add all positive numbers
sum += number;
}
// display the sum
cout << "The sum is " << sum << endl;
return 0;
}
Standard end line (endl) in C++
A predefined object of the class called iostream class is used to insert the new line characters while flushing the stream is called endl in C++. This endl is similar to \n which performs the functionality of inserting new line characters but it does not flush the stream whereas endl does the job of inserting the new line characters while flushing the stream. Hence the statement cout<<endl; will be equal to the statement cout<< '\n' << flush; meaning the new line character used along with flush explicitly becomes equivalent to the endl statement in C++.
Syntax for end line (endl) in C++
cout<< statement to be executed <<endl;
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/* Standard end line (endl) in C++ language */
//The header file iostream is imported to enable us to use cout in the program
#include <iostream>
//a namespace called std is defined
using namespace std;
//main method is called
int main( )
{
//cout is used to output the statement
cout<< "Welcome to ";
//cout is used to output the statement along with endl to start the next statement in the new line and flush the output stream
cout<< "C#"<<endl;
//cout is used to output the statement along with endl to start the next statement in the new line and flush the output stream
cout<< "Learning is fun"<<endl;
}
Vector Library size() Function in C++
Return size. Returns the number of elements in the vector. This is the number of actual objects held in the vector, which is not necessarily equal to its storage capacity. vector::size() is a library function of "vector" header, it is used to get the size of a vector, it returns the total number of elements in the vector.
The dynamic array can be created by using a vector in C++. One or more elements can be inserted into or removed from the vector at the run time that increases or decreases the size of the vector. The size or length of the vector can be counted using any loop or the built-in function named size().
Syntax for Vector size() Function in C++
#include <vector>
size_type size() const noexcept;
Complexity
Constant
Iterator validity
No changes
Data races
The container is accessed. No contained 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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/* get the size of a vector, it returns the total number of elements in the vector by vector::size() library function. */
#include <bits/stdc++.h>
using namespace std;
int main()
{
// Initializing a vector of string type
vector<string> vec = { "Happy", "8)", "Codings" };
// Clearing the vector
// Now size is equal to 0
vec.clear();
// Typecasting vec.size() to int
for (int i = 0; i < (int)vec.size() - 1; i++)
cout << vec[i] << ' ';
cout << "Happy8)Codings";
return 0;
}
Vector Library pop_back() Function in C++
Delete last element. Removes the last element in the vector, effectively reducing the container size by one. The C++ vector::pop_back function is used to delete the last element of the vector.
Every deletion of element results into reducing the container size by one unless the vector is empty. This destroys the removed element.
Syntax for Vector pop_back() Function in C++
#include <vector>
void pop_back();
Complexity
Constant
Iterator validity
The end iterator and any iterator, pointer and reference referring to the removed element are invalidated. Iterators, pointers and references referring to other elements that have not been removed are guaranteed to keep referring to the same elements they were referring to before the call.
Data races
The container is modified. The last element is modified. Concurrently accessing or modifying other elements is safe, although iterating ranges that include the removed element is not.
Exception safety
If the container is not empty, the function never throws exceptions (no-throw guarantee). Otherwise, it causes undefined behavior.
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/* push_back() function is used to push elements into a vector from the back. The new value is inserted into the vector at the end, after the current last element and the container size is increased by 1. */
/* remove last element from vector and reduces size of vector by one with std::vector::pop_back() function code example. */
#include <iostream>
#include <vector>
using namespace std;
int main (){
vector<int> MyVector{100, 200, 300, 400, 500, 600};
vector<int>::iterator it;
//deletes last element of the vector
MyVector.pop_back();
//deletes next last element of the vector
MyVector.pop_back();
cout<<"The vector contains:";
for(it = MyVector.begin(); it != MyVector.end(); ++it)
cout<<" "<<*it;
return 0;
}
Vectors in C++ Language
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.
Declaration for Vectors in C++
std::vector<T> vector_name;
Initialization for Vectors in C++
// Vector initialization method 1
// Initializer list
vector<int> vector1 = {1, 2, 3, 4, 5};
// Vector initialization method 2
vector<int> vector3(5, 12);
vector<int> vector2 = {8, 8, 8, 8, 8};
Syntax for Vector Iterators in C++
vector<T>::iterator iteratorName;
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/* Vectors in C++ language */
// C++ program to illustrate the capacity function in vector
#include <iostream>
#include <vector>
using namespace std;
int main()
{
vector<int> myvector;
for (int i = 1; i <= 5; i++)
myvector.push_back(i);
cout << "Size : " << myvector.size();
cout << "\nCapacity : " << myvector.capacity();
cout << "\nMax_Size : " << myvector.max_size();
// resizes the vector size to 4
myvector.resize(4);
// prints the vector size after resize()
cout << "\nSize : " << myvector.size();
// checks if the vector is empty or not
if (myvector.empty() == false)
cout << "\nVector is not empty";
else
cout << "\nVector is empty";
// Shrinks the vector
myvector.shrink_to_fit();
cout << "\nVector elements are: ";
for (auto it = myvector.begin(); it != myvector.end(); it++)
cout << *it << " ";
return 0;
}
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)
Direct Recursion: When function calls itself, it is called "Direct recursion". Indirect recursion: When function calls "another function" & that function calls the calling function, then this is