program makes c++ slow

[rojan1918]

So I have the following program that makes c++ slower after I run it. I think it happened after I added the NewRapHorner function and the do while loop in the main. What can be the reason and how can it be fixed?

#include <iostream>
#include <iomanip>
#include <math.h>
#define MAXGRAD 15

using namespace std;

void IndtastGrad(int &n);
void IndtastKoefficienter(double a[MAXGRAD+1], int n);
void UdskrivKoefficienter(double a[MAXGRAD+1], int n);
void UdskrivPolynomium(double a[MAXGRAD+1], int n);
void RetPolynomium(double a[MAXGRAD+1], int n);
void Horner(int n, double a[MAXGRAD], double x, double &fx, double &dfx);
void IndtastNRData(double &x0, double &eps, int &N);
void NewRapHorner(double x0, double eps, int N, int n, double a[MAXGRAD+1], double &rod, int &success);
void HornerDivPol(int &n, double a[MAXGRAD+1],double rod);

int main() {
	int n,N,success;
	double a[MAXGRAD+1],fx,dfx,x,x0,eps,rod;
	char svar;

	IndtastGrad(n);
    IndtastKoefficienter(a,n);
    UdskrivKoefficienter(a,n);
    UdskrivPolynomium(a,n);
    cout<<"Vil du gerne ændre en eller flere af koefficienterne i polynomiet?"<<endl<< "Svar j for ja eller n for nej";
    cin>>svar;
    if(svar=='j')
    RetPolynomium(a,n);
    Horner(n,a,x,fx,dfx);
    IndtastNRData(x0,eps,N);
   do{
    NewRapHorner(x0,eps,N,n,a,rod,success);
    if(success==1)
    HornerDivPol(n,a,rod);
   }while(success==1);
		return 0;
}

void IndtastGrad(int &n){
	cout<<"Indtast graden af det polynomium du vil indtaste: ";
	cin>>n;
}

void IndtastKoefficienter(double a[MAXGRAD+1], int n){
	cout<<"Indtast koefficienterne i polynomiet med koefficienten tilhørende den højeste potens først: ";

	for(int i=0; i<=n;i++)
		cin>>a[i];
	cout<<endl;
}

void UdskrivKoefficienter(double a[MAXGRAD+1], int n){
	for(int i=0; i<=n;i++)
    cout<<a[i]<<" ";

	cout<<endl;
}

void UdskrivPolynomium(double a[MAXGRAD+1], int n){
	cout<<"f(x)=";
	for(int i=0;i<=n;i++){
		cout<<a[i];
		if(n-i!=0){
			cout<<"(x^"<<n-i<<")";
		}
		if(a[i+1]>=0){
			if(i==n){
				break;
			}
		cout<<"+";

		}
	}
	cout<<endl;
}

void RetPolynomium(double a[MAXGRAD+1], int n){
	int i;
	char svar;
	do{
	cout<<"Hvilken koefficient vil du ændre?";
	cin>>i;
	cout<<"Indtast det nye tal";
	cin>>a[i-1];
	cout<<"Vil du ændre en anden koefficient eller den samme? Tryk j for ja eller n for nej";
	cin>>svar;
	}while(svar=='j');

	cout<<"Polynomiet ser nu således ud"<<endl;

	cout<<"f(x)=";
	for(int i=0;i<=n;i++){
		cout<<a[i];
		if(n-i!=0){
			cout<<"(x^"<<n-i<<")";
		}
		if(a[i+1]>=0){
			if(i==n){
				break;
			}
		cout<<"+";

		}
	}

}

void Horner(int n, double a[MAXGRAD], double x, double &fx, double &dfx){

	double A,B;

	cout<<endl<<"Indtast punktet, hvor du ønsker at finde funktionsværdien og den afledte i punktet";
	cin>>x;

	fx=a[0];
    dfx=a[0];

for(int i=0;i<n;i++){

	fx=fx*x+a[i+1];

	if(i!=n-1)
	dfx=dfx*x+fx;
	}

	cout<<"fx = "<<fx<<endl;
    cout<<"dfx = "<<dfx<<endl;

    cout<<"Indtast et interval, hvor du vil se funktionsværdien for 20 forskellige punkter"<<endl;
    cin>>A;
    cin>>B;

    cout<< setfill(' ') << setw(1) << "|" << setw(10) << left << "  x  " << setw(1) << "|" << setw(15) << left << "    fx    " << endl;

    x=A;
    for(int i=1;i<=20;i++){
    	fx=a[0];

    	if(i!=1)
    	x+=(B-A)/19;

    	for(int i=0;i<n;i++){

    		fx=fx*x+a[i+1];

    		}
	    cout << "  " <<right<< x << '\t' << "" <<setw(20)<<setprecision(20)<<right<< fx << '\t' <<endl;

    }


}

void IndtastNRData(double &x0, double &eps, int &N){
	cout<<"Indtast parametre til Newton-Raphson.\nIndtast startpunkt x0: "<<endl;
	cin>>x0;
	cout<<"Indtast tolerance eps: "<<endl;
	cin>>eps;
	cout<<"Indtast maksimalt antal tilladte iterationer N: "<<endl;
	cin>>N;
}

void NewRapHorner(double x0, double eps, int N, int n, double a[MAXGRAD+1], double &rod, int &success){

	double fx,dfx;
	int i=0;

	rod=x0;

	do{
		fx=a[0];
		dfx=a[0];

		for(int k=0;k<n;k++){

			fx=fx*rod+a[k+1];

			if(k!=n-1)
			dfx=dfx*rod+fx;
			}


		i++;
		if(dfx==0){
		break;
		}
		rod=rod-(fx/dfx);


		} while (fabs(fx)>eps and i<N);

	if(dfx==0){
			cout<<" Afslutning da dfx=0";

				}
		else if(i>=N){
			cout<<" Afslutning grundet overskridelse af max antal iterationer";
		}
		else{
		cout<<"nulpunktet til x = "<<rod<<" hvor f(x) = "<<fx;
		success=1;
		}
}

void HornerDivPol(int &n, double a[MAXGRAD+1],double rod){
	double fx;

	fx=a[0];


for(int i=0;i<n;i++){

	fx=fx*rod+a[i+1];
    a[i+1]=fx;
	}
n+=-1;
}