srand( (unsigned)time( NULL ) );
rand() % N;

 R = RAND_MAX-(RAND_MAX+1)%N; //去除尾數(shù)
  t = rand();
  while( t > R ) t = rand();
  result = t % N; // 符合要求的隨機數(shù)

 r = N % (RAND_MAX+1); //余數(shù)
  if ( happened( (double)r/N ) )//選到余數(shù)段的概率
  result = N-r+myrandom(r); // myrandom可以用情況1中的代碼實現(xiàn)
  else
  result = rand()+myrandom(N/(RAND_MAX+1))*(RAND_MAX+1); // 如果選不到余數(shù)段再進行分段選取

#include<iostream.h>
#include<time.h>
#include<stdlib.h>
const double MinProb=1.0/(RAND_MAX+1);
bool happened(double probability)//probability 0~1
{
 if(probability<=0)
 {
return false;
 }
 if(probability<MinProb)
 {
 return rand()==0&&happened(probability*(RAND_MAX+1));
 }
 if(rand()<=probability*(RAND_MAX+1))
 {
 return true;
 }
 return false;
}
long myrandom(long n)//產(chǎn)生0~n-1之間的等概率隨機數(shù)
{
 t=0;
 if(n<=RAND_MAX)
 {
 long R=RAND_MAX-(RAND_MAX+1)%n;//尾數(shù)
 t = rand();
 while ( t > r )
 {
  t = rand();
 }
 return t % n;
 }
 else
 {
 long r = n%(RAND_MAX+1);//余數(shù)
 if( happened( (double)r/n ) )//取到余數(shù)的概率
 {
  return n-r+myrandom(r);
 }
 else
 {
  return rand()+myrandom(n/(RAND_MAX+1))*(RAND_MAX+1);
 }
 }
}
 
還有另外一種非常簡單的方式，那就是使用
random_shuffle( RandomAccessIterator _First, RandomAccessIterator _Last ).
例如，生成0——N-1之間的隨機數(shù)，可以這么寫
#include <algorithm>
#include <vector>
long myrandom( long N )
{
 std::vector<long> vl( N ); // 定義一個大小為N的vector
 for ( long i=0; i<N; ++i )
 {
  vl[i] = i;
 }
 std::random_shuffle( vl.begin(), vl.end() );
 return (*vl.begin());
}
random_shuffle 還有一個三參數(shù)的重載版本
random_shuffle( RandomAccessIterator _First, RandomAccessIterator _Last, RandomNumberGenerator& _Rand )