随机函数
随机函数的实现
在编程过程中经常要用到随机数，通过调用库函数rand()来产生随机数。在调用rand()函数前一般要先调用 srand (unsigned int seed)产生随机种子。seed的选取一般可以采用系统时间来设置。产生随机数的范围在0~RAND_MAX。RAND_MAX定义在stdlib.h，其值为32767。
假如我们要产生10个0~10之间的随机数，可以通过以下方式
#include<stdlib.h>
#include<stdio.h>
#include<time.h>
main()
{
int i,j;
srand((int)time(0));
for(i=0;i<10;i++)
{
j=rand()%10;
printf(" %d ",j);
}
}
关于srand(unsigned int seed)函数和rand()函数是库函数提供给我们的接口，也可以定义自己的函数来模拟这两个函数的实现
#include <time.h>
#include <stdlib.h>
#include <stdio.h>
unsigned long int next = 1;
void LJ_srand(unsigned int seed)
{
next = seed;
}
int LJ_rand()
{
next = next*1103515+12345;
return (unsigned int)(next/65536)%32767;
}
main ()
{
int i;
LJ_srand( time(NULL) );
for( i = 0; i < 10; i++ )
printf( "Random number #%d: %d\n", i,
LJ_rand()%10);
}
rand()函数和srand()函数之间的通信是通过一个全局变量next来交互的，不调用srand()函数时，默认的next的值为1，那么每次产生的随机数是一样的。
参考c programing language
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