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Editor to share with you how to generate random numbers in the c language, I believe most people do not know much about it, so share this article for your reference. I hope you will learn a lot after reading this article. Let's learn about it.

N ways of generating Random numbers

First of all, it should be noted that the random numbers generated in the computer are strictly pseudo-random, that is, they are not real random numbers, and the random samples of real random numbers can not be reproduced. So let's take a look at the ways in the code to generate random numbers.

Rand

The rand function is declared as follows:

# include int rand (void)

The rand function returns a random integer in the range of [0mm random Max]. On my machine, the RAND_MAX is 2147483647.

Examples of use:

Rand.c * / # include # include int main (void) {int I = 0; while (I < 5) {printf ("% d", rand ()); iTunes;} printf ("\ n"); return 0;}

Compile and run:

$gcc-o rand rand.c. / rand 1804289383 846930886 1681692777 1714636915 1957747793

Run it a few more times and you will be pleasantly surprised to find that the result of each run is the same! Why don't you play with wool?

Srand

Don't worry, although the result of each run of rand is the same, that's because its seed defaults to 1. Each seed has a string of seemingly random sequences, and each time one is taken out, the whole is almost randomly distributed. But if your seed is the same every time, then the result may be the same every time you run it. We need to use srand to give it a seed.

# include void srand (unsigned int seed)

In order to ensure that the random number we get is different each time, we have to make sure that the seed is different with each call, so we usually choose to use time as the seed, note that this is only the usual seed choice, you can choose according to the actual use needs.

So we set up the seed before using it, using the example:

Rand.c * / # include # include # include int main (void) {srand (time (NULL)); / / set random seed, note that you only need to set it once to int I = 0; while (I < 5) / / generate 5 random numbers {printf ("% d", rand ()); iTunes;} printf ("\ n"); return 0;}

Now, the generation is different each time you run it. But there is another problem, and if this approach is used in multithreading, it is not desirable because rand is not a reentrant function. Each call to it modifies some hidden properties, so it is not appropriate to use it in multithreading.

Rand_r

To use it in multithreading, we use rand_r in the same way as rand:

# include int rand_r (unsigned int * seedp)

Examples of use:

# include # include # include int main (void) {unsigned int seed = time (NULL); int I = 0; while (I < 5) / / generate 5 random numbers {printf ("% d", rand_r (& seed)); iTunes;} printf ("\ n"); return 0;}

In multithreading, multiple threads may call almost simultaneously, so their seeds may also be the same, and if you want to be different, you can also set the seeds to be related to the thread id.

Unsigned int seed = time (NULL) ^ pthread_self ()

Random

From the previous example, we can see that the range of integers generated by rand is limited, and to generate a larger range, you can use random:

# include long int random (void); void srandom (unsigned int seed)

The type returned by random is long int, so to some extent, it generates a much larger range. Also similar to rand, you need to set the seed using the srandom function. Specific examples will no longer be released.

Generate a random number with a specified range

The previous examples are all about generating numbers between [1]. What if you want to generate random numbers with a specified interval? Assume that an and b do not exceed the int range and that their differences do not exceed the rand generation range.

[a _ dint _ b)

Left closed and right open interval, that is, contains a, does not contain:

(rand ()% (b-a)) + a

[a,b]

Left and right closed, that is, including an and b:

(rand ()% (b-a + 1)) + a

(a dint b)

Open left and close right, that is, it does not contain a, including b:

(rand ()% (bmura)) + a + 1

[0,b]

Rand () b

Floating point number between 0 and 1

Rand () / (double) RAND_MAX

Give an example

Generate 5 random numbers between [2 and 10):

# include # include # include int main (void) {srand (time (NULL)); / / set random seeds. Note that int I = 0; int a = 2; int b = 10; while (I < 5) / / generate 5 random numbers {printf ("% d", (rand ()% (b-a)) + a) } printf ("\ n"); return 0;} above is all the content of the article "how to generate random numbers in c language". Thank you for reading! I believe we all have a certain understanding, hope to share the content to help you, if you want to learn more knowledge, welcome to follow the industry information channel!

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