顺序求出c(n,r)的排列组合

namespace combinaton
{
 /// <summary>
 /// Summary description for Class1.
 /// </summary>
 class Class1
 {
  /// <summary>
  /// The main entry point for the application.
  /// </summary>
  [STAThread]
  static void Main(string[] args)
  {
//
// TODO: Add code to start application here
//
Console.WriteLine("please input n :");
long n=long.Parse(Console.ReadLine());
Console.WriteLine("please input r :");
long r=long.Parse(Console.ReadLine());
combinaton(n,r);
Console.ReadLine();
  }
  static void combinaton(long n,long r)
  {
if(n<r)
{
 long temp;
 temp=n;
 n=r;
 r=temp;
}
long[] s=new long[n];
long count = combi(n,r);
Console.WriteLine("there are total:{0}count:",count);
for(long i=0;i<r;i++)
{
 s[i]=i+1;
 Console.Write("{0}",s[i]);
}
Console.WriteLine();
for(long i=1;i<count;i++)
{
 long m=r-1,max_value=n;
 while(s[m]==max_value)
 {
  m=m-1;
  max_value=max_value-1;
 }
 s[m]=s[m]+1;
 for(long j=m+1;j<r;j++)
 {
  s[j]=s[j-1]+1;
 }
 for(long k=0;k<r;k++)
 {
  Console.Write("{0}",s[k]);
 }
 Console.WriteLine();
}
  }

//compute value of c(n,r)
  static long combi(long n,long r)
  {
long sn=1,sr=1,s_r=1;
for(long i=1;i<=n;i++)
{
 sn*=i;
}
for(long j=1;j<=r;j++)
{
 sr*=j;
}
for(long k=1;k<=n-r;k++)
{
 s_r*=k;
}
sr*=s_r;
return sn/sr;
  }
 }
}