Why Does Repeatedly Using `srand()` in a C Function Lead to Non-Random Results?

Using rand() to Generate Truly Random Values Within a Function

In C , using rand() to generate random numbers within a single function can result in recurring values. This issue arises when srand() is repeatedly invoked before each call to rand().

Problem:

Consider the example you provided:

string PullOne()
{
    string pick;
    string choices[3] = {"BAR", "7", "cherries"};

    std::srand(time(0));
    pick = choices[(std::rand() % 3)];
    return pick;
}

When calling PullOne() multiple times from within main(), you expect distinct random values for pull_1, pull_2, and pull_3. However, you're consistently obtaining identical results.

Solution:

To remedy this, move the invocation of srand() outside of the PullOne() function and place it once at the outset of your program. By doing so, you initialize the random number generator once, ensuring a truly random sequence is produced for subsequent rand() calls.

// srand() is now called only once, at program initialization.
int main()
{
    std::srand(time(0));

    string pull_1, pull_2, pull_3;
    pull_1 = PullOne();
    pull_2 = PullOne();
    pull_3 = PullOne();

    return 0;
}

Explanation:

srand() sets the seed for the random number generator. When the same seed is repeatedly used, the generator produces the same sequence. By initializing srand() once, the seed is consistent throughout the program, leading to a predictable and non-random output from rand().

Therefore, it's crucial to call srand() only once, ideally during program initialization or at the start of the random number generation process. This ensures the generation of truly random numbers within your function.

The above is the detailed content of Why Does Repeatedly Using `srand()` in a C Function Lead to Non-Random Results?. For more information, please follow other related articles on the PHP Chinese website!