How to print commas ONLY if the user input is in the thousands

[BorgQueen]

Hi, I am in a first year C++ class. I am writing a program that is supposed to contain a flexible, general algorithm for base conversions. I am satisfied with my algorithm, but I am having difficulty meeting all of my instructors criteria. I need to print a comma in my decimal output if the number to be converted is in the ten thousands. Below is my code, and I have taken out the user prompt and just hard set a value to be converted in the main function (the maximum value)

for clarity, here is my instructor's criteria:
http://mylinux.langara.bc.ca/~peterbaker/Courses/CpSc1155-IntroCpp/CPSC-1155-Cpp-PB-Lab7.pdf

NOTE: I am only working on the converter part of this assignment, I still have a lot more work to do, obviously.

#include <iostream>
using namespace std;

int converter (int userInput) {
   int qtnt;
   int dat = userInput;
   int hexData [4];
   int binData [16];
   int octData [ 6 ];
   int decData [ 5 ];
   while (dat != -1) {// While loop: Runs conversion statements
      if (dat == -1) {// If statement: Exits if input it negative 1
         return 0;// Ends program
      }
      if (dat >= 0 && dat <= 65535) { // If statement: executes conversion statements if user input is valid
         qtnt = dat; // set quotient to user input
            for (int counter = 0; counter < 5; counter++) { // populate decimal array
               decData[counter] = qtnt % 10;
               qtnt = qtnt / 10;
            }
      cout << "In Decimal:         ";
      for (int counter = 4; counter >= 0; counter--) { // // prints most significant bit first
         if (decData[counter] == 0) { // eliminate leading zeros
            cout <<"";
         }
         else {     
///////////////////////////// (figure out how to print comma)      <-----------------------------------      
            cout << decData[counter];//print current digit
         }
      }
      cout << endl;
      qtnt=dat;//reset qtnt to user input
      for (int counter = 0; counter < 4; counter++) {// populate hex array
         hexData[counter] = qtnt % 16;
         qtnt = qtnt / 16;
      }
      cout <<"In Hexidecimal:   ";
      for (int counter = 3; counter >= 0; counter--) {// prints most significant bit first
         if (hexData[counter] == 0) {//eliminate leading zeros
            cout <<"";
         }
         else if (hexData[counter] > 9) {//print ascii characters for hex digits over 9
            char hex = (char)hexData[counter] + 55;
            cout << hex;
         }         
         else { //print current hex digit less than 9
            cout << hexData[counter];
         }
      }
      qtnt= dat;// reset qtnt to user input
      for (int counter = 0; counter < 16; counter++) {// populate binary array
         binData[counter] = qtnt % 2;
         qtnt = qtnt / 2;
      }
      cout << endl;
      cout << "In Binary:           ";
      for (int counter = 15; counter >= 0; counter--) {// prints most significant bit first
         if (counter < 15 && counter % 4 == 3) {// print dashes for every 4 bits
            cout << "-";
         }
         cout << binData[counter];//print current binary digit
      }
      cout << endl;
      qtnt= dat;
      for (int counter = 0; counter < 6; counter++) { //populate octal array
         octData[counter] = qtnt % 8;
         qtnt = qtnt / 8;
      }
      cout << "In Octal:            ";
      for (int counter = 5; counter >= 0; counter--) {// prints most significant bit first
         if (octData[counter] == 0) {//eliminate leading zeros
            cout <<"";
         }
         else {            
            cout << octData[counter];
         }  
      }
      cout << endl;
      return 0;
      } // end if statement
   } // end while loop
} // end converter function

int main(){
   int input = 65535;// this would be "cin" on final program, preceded by a prompt
   converter (input);
   return 0; 
}

thank you very much for any suggestions.