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/*	Name:		find_nbr.c *	Purpose:	This program picks a random number and then *				lets the user try to guess it *	Returns:	Nothing */#include 
    
     #include 
     
      #include 
      
       #define NO 0#define YES 1int main(void){	int guess_value = -1;	int number;	int nbr_of_guesses;	int done = NO;	printf("\n\nGetting	a Random number\n");	/* use the time to seed the random number generator*/	srand(	(unsigned) time(	NULL ) );	number = rand();	nbr_of_guesses = 0;	while ( done == NO)	{		printf("\nPick a number between 0 and %d> ",RAND_MAX);		scanf(	"%d",	&guess_value); /*Get a number*/		nbr_of_guesses++;		if ( number == guess_value)		{			done = YES;		}		else		if ( number < guess_value)		{			printf("\nYou guessed high !");		}		else		{			printf("\nYou guessed low!");		}	}	printf("\n\nCongratulations ! You guessed right in %d Guesses! ",			nbr_of_guesses);	printf("\n\nThe number was %d\n\n",number);	return 0;}
      
     
    

srand()就是给rand()提供种子seed

如果srand每次输入的数值是一样的，那么每次运行产生的随机数也是一样的，

也就是说，以一个固定的数值作为种子是一个缺点。 通常的做法是  以这样一句代码srand((unsigned) time(NULL));来取代，这样将使得种子为一个不固定的数， 这样产生的随机数就不会每次执行都一样了。

/* RAND.C: This program seeds the random-number generator * with the time, then displays 10 random integers. */#include 
   
    #include 
    
     #include 
     
      void main( void ){   int i;   /* Seed the random-number generator with current time so that    * the numbers will be different every time we run.    */   srand( (unsigned)time( NULL ) );   /* Display 10 numbers. */   for( i = 0;   i < 10;i++ )      printf( "  %6d\n", rand() );}
     
    
   

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