🚀 go-pugleaf

My home network has one DSL modem, one router and two PCs.
Each PC attached to the router has an IP address, 192.168.0.x .
The router is attached to the DSL modem. 

I need the public IP address of the router.
So, I make following codes and run it from one of my home network PC.
But, it displays private IP address.
How can I get the public IP address of the router?

#include<winsock2.h>
#include<stdio.h>
#include<iostream>
#include "iphlpapi.h"

using namespace std;

#pragma link "iphlpapi.lib"

#pragma argsused
int main(int argc, char* argv[])
{
 ShowIpNetTable();
 return 0;
}

void ShowIpNetTable()
{
 DWORD size=0;
 char buff[512];
 GetIpNetTable((MIB_IPNETTABLE*)buff,&size,true);
 if(size==0) return;
 char* raw_buff = new char[size];
 MIB_IPNETTABLE* pmib_ipnettable=(MIB_IPNETTABLE*)raw_buff;
 if(ERROR_INSUFFICIENT_BUFFER!=GetIpNetTable(pmib_ipnettable,&size,true))
 {
  for(DWORD i=0; i<pmib_ipnettable->dwNumEntries; ++i)
  {
    cout << "IpNet" << (pmib_ipnettable->table[i].dwIndex) << ": " << endl;
    cout << "  MAC = " << StrMacAddrFromBytes(pmib_ipnettable->table[i].bPhysAddr ,pmib_ipnettable->table[i].dwPhysAddrLen,buff) << endl;
    cout << "  IP  = " << DottedBytesFromDword(pmib_ipnettable->table[i].dwAddr,buff) << endl;
    cout << "  Type= " << HexFromDword(pmib_ipnettable->table[i].dwType,buff) << endl;
  }
 }
 delete[] raw_buff;
}

char *StrMacAddrFromBytes(const BYTE* bytes,int size,char*outbuff)
{
  for(int i=0 ;i<size ;++i)
  {
     sprintf(outbuff+i*3,"%02X:",bytes[i]);
  }
  outbuff[size*3-1]=0;
  return outbuff;
}

char* DottedBytesFromDword(DWORD ip,char*outbuff)
{
 unsigned char *p = (char*)&ip;
 int n=0;
 for(int i=0 ;i<sizeof(DWORD) ;++i)
 {
  n += sprintf(outbuff+n,"%u.",p[i]);
 }
 outbuff[n-1]=0;
 return outbuff;
}

char* HexFromDword(DWORD num,char *outbuff)
{
 sprintf(outbuff,"%X",num);
 return outbuff;
}