'foo' n'a pas été déclarée dans ce champ d'application c++

Je suis en train d'apprendre le c++ (premier jour de la regarder depuis que j'ai pris 1 semaine de camp d'été il y a des années)

J'ai été la conversion d'un programme que je suis en train de travailler avec Java C++:

#ifndef ADD_H
#define ADD_H
#define _USE_MATH_DEFINES
#include <iostream>
#include <math.h>
using namespace std;
class Evaluatable {
public:
virtual double evaluate(double x);
};
class SkewNormalEvalutatable : Evaluatable{
public:
SkewNormalEvalutatable();
double evaluate(double x){
return 1 / sqrt(2 * M_PI) * pow(2.71828182845904523536, -x * x / 2);
}
};
SkewNormalEvalutatable::SkewNormalEvalutatable()
{
}
double getSkewNormal(double skewValue, double x)
{
SkewNormalEvalutatable e ();
return 2 / sqrt(2 * M_PI) * pow(2.71828182845904523536, -x * x / 2) * integrate(-1000, skewValue * x, 10000, e);
}
//double normalDist(double x){
//  return 1 /Math.sqrt(2 * Math.PI) * Math.pow(Math.E, -x * x /2);
//}
double integrate (double start, double stop,
int numSteps, 
Evaluatable evalObj)
{
double stepSize = (stop - start) / (double)numSteps;
start = start + stepSize / 2.0;
return (stepSize * sum(start, stop, stepSize, evalObj));
}
double sum (double start, double stop,
double stepSize,
Evaluatable evalObj)
{
double sum = 0.0, current = start;
while (current <= stop) {
sum += evalObj.evaluate(current);
current += stepSize;
}
return(sum);
}
//int main()
//{
//  cout << getSkewNormal(10.0, 0) << endl;
//  return 0;
//}
#endif

Les erreurs ont été:

SkewNormal.h: In function 'double getSkewNormal(double, double)' :
SkewNormal.h: 29: error: 'integrate' was not declared in this scope
SkewNormal.h: In function 'double integrate(double, double, int, Evaluatable)':
SkewNormal.h:41: error: 'sum' was not declared in this scope

Intégrer et de la somme sont censés être des fonctions

Voici le code Java, plus ou moins le même:

public static double negativelySkewed(double skew, int min, int max){
return randomSkew(skew) * (max - min) + min;
}
public static double randomSkew(final double skew){
final double xVal = Math.random();
return 2 * normalDist(xVal) * Integral.integrate(-500, skew * xVal, 100000, new Evaluatable() {
@Override
public double evaluate(double value) {
return normalDist(value);
}
});
}
public static double normalDist(double x){
return 1 / Math.sqrt(2 * Math.PI) * Math.pow(Math.E, -x * x / 2);
}
/** A class to calculate summations and numeric integrals. The
*  integral is calculated according to the midpoint rule.
*
*  Taken from Core Web Programming from 
*  Prentice Hall and Sun Microsystems Press,
*  http://www.corewebprogramming.com/.
*  © 2001 Marty Hall and Larry Brown;
*  may be freely used or adapted. 
*/
public static class Integral {
/** Returns the sum of f(x) from x=start to x=stop, where the
*  function f is defined by the evaluate method of the 
*  Evaluatable object.
*/
public static double sum(double start, double stop,
double stepSize,
Evaluatable evalObj) {
double sum = 0.0, current = start;
while (current <= stop) {
sum += evalObj.evaluate(current);
current += stepSize;
}
return(sum);
}
/** Returns an approximation of the integral of f(x) from 
*  start to stop, using the midpoint rule. The function f is
*  defined by the evaluate method of the Evaluatable object.
*/
public static double integrate(double start, double stop,
int numSteps, 
Evaluatable evalObj) {
double stepSize = (stop - start) / (double)numSteps;
start = start + stepSize / 2.0;
return(stepSize * sum(start, stop, stepSize, evalObj));
}
}
/** An interface for evaluating functions y = f(x) at a specific
*  value. Both x and y are double-precision floating-point 
*  numbers.
*
*  Taken from Core Web Programming from 
*  Prentice Hall and Sun Microsystems Press,
*  http://www.corewebprogramming.com/.
*  &copy; 2001 Marty Hall and Larry Brown;
*  may be freely used or adapted. 
*/
public static interface Evaluatable {
public double evaluate(double value);
}

Je suis certain que c'est quelque chose de très simple

Aussi, comment dois-je appeler

getSkewNormal(double skewValue, double x)

À partir d'un fichier en dehors de SkewNormal.h?