C++ Programming Code Examples
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Demonstrate count() in vector
/* Demonstrate count() in vector */
#include <iostream>
#include <vector>
#include <cstdlib>
#include <algorithm>
using namespace std;
int main()
{
vector<bool> vectorObject;
int i;
for(i = 0; i < 10; i++) {
if(rand() % 2)
vectorObject.push_back(true);
else
vectorObject.push_back(false);
}
cout << "Sequence:\n";
for(i = 0; i <vectorObject.size(); i++)
cout << boolalpha << vectorObject[i] << " ";
cout << endl;
i = count(vectorObject.begin(), vectorObject.end(), true);
cout << i << " elements are true.\n";
return 0;
}
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. The vector class provides various methods to perform different operations on vectors. Add Elements to a Vector: To add a single element into a vector, we use the push_back() function. It inserts an element into the end of the vector. Access Elements of a Vector: In C++, we use the index number to access the vector elements. Here, we use the at() function to access the element from the specified index.
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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(). This function does not accept any parameter.
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. Function returns the element at the specified position in the vector.
#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.
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. This function does not return any value.
Count appearances of value in range. Returns the number of elements in the range [first,last) that compare equal to val. The function uses operator== to compare the individual elements to val. The C++ function std::algorithm::count() returns the number of occurrences of value in range. This function uses operator == for comparison. Function returns the number of elements in the range [first,last) that compare equal to val. The return type (iterator_traits<InputIterator>::difference_type) is a signed integral type.
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.
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. This function does not accept any parameter.
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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.
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. This function does not accept any parameter.
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Class for addition, subtraction, multiplication and division for 'complex numbers'. Class has 4 functions to perform arithmetic operations. It takes 2 "complex numbers" input from user
