C / C++ / MFC

#include <stdio.h>
#include "../include/ESSolver.h"

int mu;
int lambda ;

int main(void)
{	
	mu        = 5;
	lambda    = 10;
	
	ESSolver es;

	es.Init();
	
	es.Optimize();
		
	return 0;
}

extern int mu;
extern int lambda ;

class ESSolver
{
public:
	const static int nVar = 4;
	
	ESSolver();
	~ESSolver(void);
	
    void Init();
    void Optimize();
    int rand_r(int, int);
    
private:
	double (*muPop)[nVar];
	double *muSigma;     
	
	double (*lambdaPop)[nVar];
	double *lambdaSigma;
	
	double (*mulambdaPop)[nVar];
	double *mulambdaSigma;
};

#include <iostream>
#include <cmath>
#include <vector>
#include <algorithm>
#include <queue>

#include "../include/ESSolver.h"

using namespace std;

ESSolver::ESSolver()
{
	double _muPop [mu][nVar];
	muPop   = _muPop;
	muSigma = new double[mu];
		
	double _lambdaPop [lambda][nVar];
	lambdaPop   = _lambdaPop;
	lambdaSigma = new double[lambda];
		
	double _mulambdaPop [mu+lambda][nVar];
	mulambdaPop   = _mulambdaPop;
	mulambdaSigma = new double[mu+lambda];
	
	return;
}

ESSolver::~ESSolver(void)
{
	if (muSigma) delete muSigma;
	if (lambdaSigma) delete lambdaSigma;
	if (mulambdaSigma) delete mulambdaSigma;
	return;
}

void ESSolver::Init()
{
	// Initializing object variable
	for (int i = 0; i < mu; i++)
	{
		for (int j = 0; j < nVar; j++)
		{
			muPop[i][j] = 50;
		}
	}
	
	cout << "\n----- muPop -----\n";
	for (int i = 0; i < mu; i++)
	{
		for (int j = 0; j < nVar; j++)
		{
			cout << muPop[i][j] << " ";
		}
		cout << endl;
	}
	
}

void ESSolver::Optimize()
{
	cout << "\n----- muPop -----\n";
	for (int i = 0; i < mu; i++)
	{
		for (int j = 0; j < nVar; j++)
		{
			cout << muPop[i][j] << " ";
		}
		cout << endl;
	}
}

#include <vector>
#include <iostream>

using namespace std;

int main()
{
  double arr[] = {0.2, 1.0, 0.01, 3.0, 0.002, -1.0, -20};
  
  priority_queue < pair<double, int> > pQueue;
  
  for (int i = 0; i < 7; i++) 
  {
    pQueue.push(pair<double, int>(arr[i], i));
  }
  
  int k = 3; // number of indices we need
  
  for (int i = 0; i < k; ++i) 
  {
    int ki = pQueue.top().second;
    cout << ki << " ";
    pQueue.pop();
  }
  
}

Hi,

I am a newbee to c++. 
iostream include definition of cout and cin
But if I write cout without std, It throws error, which should be corrcted to std::cout.
Why so?