count_if c++ example

c++ > algorithm > count_if

count_if returns the number of elements in a range whose values satisfy a specified condition.

template<class InputIterator, class Predicate>
   typename iterator_traits<InputIterator>::difference_typecount_if(
      InputIterator _First, 
      InputIterator _Last,
      Predicate _Pred
   );

Example

#include "stdafx.h"

#include <iostream>

#include <algorithm> 

#include <vector> 

using namespace std;

bool IsEven(int n)

{

       return ((n % 2) == 0);

}

int main() {

       std::vector<int> numbers;

       for (int i = 1; i<10; i++)

              numbers.push_back(i);

       int evencount = count_if(numbers.begin(), numbers.end(), IsEven);

       std::cout << "numbers contains " << evencount << " even values.\n";

       return 0;

}

Result:

C++ Pointers Example

C++ > Pointers

Syntax:

type * name;

A variable which stores the address of another variable is called a pointer.

Pointers point to the variable whose address they store.

Example

#include "stdafx.h"

int main()

{

       int var = 25;

       int *adr = &var;

       // *adr = 25

       // adr   = 0x0042fc1c

       *adr = 30;

       // var = 30

    return 0;

}

C++ Map class emplace example

C++ > Map class > Emplace

Inserts an element constructed in place into a map.

Example 

// ConsoleApplication1.cpp : Defines the entry point for the console application.

//

#include "stdafx.h"

#include <map>

#include <string>

#include <iostream>

using std::endl;

using std::cout;

using std::cin;

int _tmain(int argc, _TCHAR* argv[])

{

       std::map <int, std::string> map;

       auto ret1 = map.emplace(1, "one");

       auto ret2 = map.emplace(2, "two");

       auto tree1 = *ret1.first;

       auto tree2 = *ret2.first;

       cout << "First element is (" << tree1.first << ", " << tree1.second << ")" << endl;

       cout << "Second element is (" << tree2.first << ", " << tree2.second << ")" << endl;

       int ret;

       cin >> ret;

       return ret;

}

#pragma once C# example

C++ > Pragma directives > #pragma once

Specifies that the file will be included only once by the compiler when compiling a source code file, so the build times is reduced.

Example:

HeaderClass.h

#pragma once

// Code placed here is included only once 

namespace Application{

class HeaderClass

{

public:

    HeaderClass();

};

} // namespace Application