Octal to Binary number converter

#include < iostream.h >
void main ()
{
 const int converts = 10;

  for (int ctr = 1;ctr <= converts; ctr++)
  {
 int dec = 0, mult = 1, prod = 0, rem, oct, px, chk;
 bool isoctal = true;
 
 cout << "Enter a valid Octal Number: ";
 cin >> oct;
 
 px = oct;

 while (px > 0)
 {
  chk = px % 10;
  if (chk >= 8)
  {
   isoctal = false;
   cout << "Invalid Octal Number\n\n";
   break;
  }
  px = px / 10;
 }

 if (isoctal)
 {
 while (oct > 0)
 {
  rem = oct % 10;
  prod = rem * mult;
  dec = dec + prod;
  mult = mult * 8;
  oct = oct / 10;
 }

 mult = 1;

 while (dec > 0)
 {
  rem = dec % 2;
  prod = rem * mult;
  oct = oct + prod;
  mult = mult * 10;
  dec = dec / 2;
 }

 cout << "The Binary equivalent is: " << oct << "\n\n";
 }
 
  }
}

source: http://www.planetsourcecode.com/