Function to generate all possible Mathematical Combination of numbers

import java.io.*;

class combination
{
    public static void main(String args[])throws IOException
    {
 DataInputStream in;
 String s;
 int a,n,r;

 System.out.print("Enter the value of n : ");
 in = new DataInputStream(System.in);
 s = in.readLine();
 n = Integer.parseInt(s);

 System.out.print("Enter the value of r : ");
 in = new DataInputStream(System.in);
 s = in.readLine();
 r = Integer.parseInt(s);


 if(n < r)
     System.out.println("\n\t\tCheck the input.\n");


 else
 {
     int i,j;
     String v[] = new String[n];

     System.out.println("Enter the n's : ");
     for(i = 0; i < n; i++)
     {
  in = new DataInputStream(System.in);
  s = in.readLine();
  v[i] = s;
     }


     int temp[] = new int[r], q;
     boolean f = false;


     for(i = 0; i < r; i++)
  temp[i] = i;

     System.out.println("\nThe Combinations are :\n");
     a = 1;

     while(temp[0] <= n - r)
     {
  while( temp[r - 1] < n )
  {
      for(j = 0; j < r; j++)
   System.out.print(" " + v[ temp[j] ] + ",");

      System.out.print("  -  " + a++);

      in.readLine();

      temp[r - 1] += 1;
  }

  for(j = r - 1, i = 0, f = false; j > 0 && f == false; i++,j--)
      if(temp[j] <= n)
   f = true;

  for(i = j, q = temp[j]; i < r; i++)
          temp[i] = q + i - j + 1;
     }
 }
    }
}