C语言 在c中生成1到10之间的随机数
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generate a random number between 1 and 10 in c
提问by Nisarg
#include <stdio.h>
#include <stdlib.h>
int main()
{
int randomnumber;
randomnumber = rand() % 10;
printf("%d\n", randomnumber);
return 0;
}
This is a simple program where randomnumber is an uninitialized int variable that is meant to be printed as a random number between 1 and 10. However, it always prints the same number whenever I run over and over again. Can somebody please help and tell me why this is happening? Thank you.
这是一个简单的程序，其中 randomnumber 是一个未初始化的 int 变量，旨在作为 1 到 10 之间的随机数打印。但是，每当我一遍又一遍地运行时，它总是打印相同的数字。有人可以帮忙告诉我为什么会这样吗？谢谢你。
采纳答案by ouah
You need a different seed at every execution.
每次执行都需要不同的种子。
You can start to call at the beginning of your program:
您可以在程序开始时开始调用：
srand(time(NULL));
Note that % 10yields a result from 0to 9and not from 1to 10: just add 1to your %expression to get 1to 10.
需要注意的是% 10产生从结果0来9，而不是来自1于10：只需添加1到您的%表达让1到 10。
回答by Byusa
srand(time(NULL));
int nRandonNumber = rand()%((nMax+1)-nMin) + nMin;
printf("%d\n",nRandonNumber);
回答by dang
Here is a ready to run source code for random number generator using c taken from this site: http://www.random-number.com/random-number-c/. The implementation here is more general (a function that gets 3 parameters: min,max and number of random numbers to generate)
这是一个准备运行的随机数生成器源代码，使用来自本站点的 c：http: //www.random-number.com/random-number-c/。这里的实现更通用（一个函数，它获取 3 个参数：min、max 和要生成的随机数的数量）
#include <time.h>
#include <stdlib.h>
#include <stdio.h>
// the random function
void RandomNumberGenerator(const int nMin, const int nMax, const int nNumOfNumsToGenerate)
{
int nRandonNumber = 0;
for (int i = 0; i < nNumOfNumsToGenerate; i++)
{
nRandonNumber = rand()%(nMax-nMin) + nMin;
printf("%d ", nRandonNumber);
}
printf("\n");
}
void main()
{
srand(time(NULL));
RandomNumberGenerator(1,70,5);
}
回答by Macattack
You need to seed the random number generator, from man 3 rand
您需要为随机数生成器提供种子，从 man 3 rand
If no seed value is provided, the rand() function is automatically seeded with a value of 1.
如果未提供种子值，则 rand() 函数将自动以 1 值作为种子。
and
和
The srand() function sets its argument as the seed for a new sequence of pseudo-random integers to be returned by rand(). These sequences are repeatable by calling srand() with the same seed value.
srand() 函数将其参数设置为 rand() 返回的新伪随机整数序列的种子。这些序列可以通过使用相同的种子值调用 srand() 来重复。
e.g.
例如
srand(time(NULL));
回答by Lee Daniel Crocker
Generating a single random number in a program is problematic. Random number generators are only "random" in the sense that repeated invocations produce numbers from a given probability distribution.
在程序中生成单个随机数是有问题的。随机数生成器只是“随机”，因为重复调用会根据给定的概率分布生成数字。
Seeding the RNG won't help, especially if you just seed it from a low-resolution timer. You'll just get numbers that are a hash function of the time, and if you call the program often, they may not change often. You might improve a little bit by using srand(time(NULL) + getpid())(_getpid()on Windows), but that still won't be random.
播种 RNG 无济于事，尤其是如果您只是从低分辨率计时器中播种。您只会得到作为时间散列函数的数字，如果您经常调用该程序，它们可能不会经常更改。您可能会通过使用srand(time(NULL) + getpid())(_getpid()在 Windows 上)来改进一点，但这仍然不是随机的。
The ONLY way to get numbers that are random acrossmultiple invocations of a program is to get them from outside the program. That means using a system service such as /dev/random(Linux) or CryptGenRandom()(Windows), or from a service like random.org.
只有这样，才能让那些随机数跨越多个调用的程序是从程序以外得到他们。这意味着使用诸如/dev/random(Linux) 或CryptGenRandom()(Windows) 之类的系统服务，或来自诸如random.org.
