conversiones a base octal, binario y hexadecimal

aquí el código en dev c++
//conversiones a base octal, binario y hexadecimal
#include<iostream>
#include<stdio.h>
#include<conio.h>
#include<stdlib.h>
#include<windows.h>
using namespace std;
void gotoxy(int x,int y){ 
      HANDLE hcon; 
      hcon = GetStdHandle(STD_OUTPUT_HANDLE); 
      COORD dwPos; 
      dwPos.X = x; 
      dwPos.Y= y; 
      SetConsoleCursorPosition(hcon,dwPos);
  }
int main(){

int n,a,b,col=40,op,ren=3;
gotoxy(2,1);cout<<"que numero desea convertir: ";
cin>>n;
    system("cls");
gotoxy(2,2);cout<<"A que base desea convertirlo: ";
gotoxy(2,3);cout<<"[1 binario ";
    gotoxy(2,4);cout<<"[2 octal ";
gotoxy(2,5);cout<<"[3 hexadecimal ";
gotoxy(2,6);cout<<"[4 salir ";
cin>>op;
getch();
system("cls");
      switch (op)
{
while(op!=0){

case 1:
while(n>0){
a=n%2;
gotoxy(col,ren);cout<<a;
n=n/2;

col=col-2;

}
case 2:
while(n>0){
a=n%8;
gotoxy(col,ren);cout<<a;
n=n/8;
col=col-2;}
case 3:
while(n>0){
a=n%16;
n=n/16;
col=col-2;
switch(a){
   case 10:
    gotoxy(col,ren);cout<<"A";
    break;
    case 11:
    gotoxy(col,ren);cout<<"B";
    break;
    case 12:
    gotoxy(col,ren);cout<<"C";
    break;
    case 13:
    gotoxy(col,ren);cout<<"D";
    break;
    case 14:
    gotoxy(col,ren);cout<<"E";
    break;
    case 15:
    gotoxy(col,ren);cout<<"F";
    break;
   default:
    gotoxy(col,ren);cout<<a;
   }
}
case 4:
op=0;
break;
}
}
}