#include <stdlib.h>
  void srand( unsigned seed );

The function srand() is used to seed the random sequence generated by rand(). For any given seed, rand() will generate a specific "random" sequence over and over again.

   srand( time(NULL) );
   for( i = 0; i < 10; i++ )
     printf( "Random number #%d: %d\n", i, rand() );