Getting the same answer, when the program restarts

Well i've made a program that asks the decimal number, and puts it in a numberStelsel.
BUt my problem is that it doenst work properly.
for example
Decimal number = 16
Numberstelsel= 8
I get: 20

This is correct
After i push de Y, to let the program start again.
I insert
Decimal number = 15
Numberstelsel= 5
I get: 20

This is the wrong number + its the same answer of the one before this.
Can someone help me with this one?

Code:

#include <stdio.h>
#include <conio.h>

/* definition of functions: */
int Input(void);
void DecimalToBinary(double *);
void Output(double);

/* variables declare*/
int nDecimal = -1, nStelsel;
double dRem , dPow_10 = 1, dBinary;
char chAgain = 'y';

int main()
{
while(chAgain=='y')
	{
		nDecimal = Input();
   	printf("\nVoer het getalstel in:\n");
		scanf("%d",&nStelsel);
		while(nStelsel < 2 || nStelsel >= 10)
		{
			printf("Voer een getalstelsel tussen de 1 en de 10:");
			scanf("%d", &nStelsel);
		}
		DecimalToBinary(&dBinary);
		Output(dBinary);
		printf("Do you want to run this program again? [y/n]: ");
   	chAgain = getch();
	}


	/* exit program */
	return 0;
}

int Input(void)
/****************************************************|
|Function: Hier word het decimale getal gekozen.     |
|Argument: geen                                      |
|return:   nDecimal                                  |
\****************************************************/
{

	while((nDecimal < 0) || (nDecimal > 1023))
	{
      printf("Dit programma rekent een decimaal getal om naar een getal \nin de door uw ingevoerde getalstelsel\n");
		printf("Your decimal number (0 .. 1023): ");
		scanf("%d",&nDecimal);
	}
return nDecimal;
}

void Output(double dBinary)
/*******************************************|
|Function: Print de waarde uit              |
|Argument: dBinary                           |
|Return: geen                                 |
\*******************************************/

{
	printf("The value is: %10.0lf\n",dBinary);
}

void DecimalToBinary(double *pBinary)
/*********************************************\
|Function: Rekent het om in het getalstelsel  |
|Argument: nDecimal                            |
|Return:   dBinary                              |
\*********************************************   */       
{
	while(nDecimal != 0)
	{
		dRem = nDecimal % nStelsel;
		nDecimal = nDecimal / nStelsel;
		*pBinary = dBinary + (dRem * dPow_10);
		dPow_10 = dPow_10 * 10;
	}
}

Well, once your Input function retrieves a valid input it will keep returning that one. Look closer on this function.
Oh, and this is a C# forum, not C++.