Why Does Repeated `rand()` Usage in C Produce Predictable Sequences?

Random Initialization Issue within Function Calls

In C , the rand() function is commonly used to generate random numbers. However, when called repeatedly within a single function, it can produce predictable sequences instead of true randomness. This behavior can be troublesome when requiring multiple unique random values.

To rectify this issue, you should avoid initializing the random generator srand() before each rand() call. Instead, it should be done only once, preferably at the start of the program.

Problem Explanation

The reason for the unpredictable sequence is that srand() seeds the random generator with a specific value. Subsequent calls within the same function will use the same seed, leading to a consistent sequence of random numbers. By initializing the generator only once, it ensures that a unique seed is used for the entire program.

Revised Code:

int GenerateRandomNumber()
{
    static bool srand_initialized = false;

    if (!srand_initialized)
    {
        srand(time(0));  // Initialize random generator once
        srand_initialized = true;
    }

    return rand() % 3;
}

In this updated code, srand() is initialized only once before the first call to GenerateRandomNumber(). This ensures that each call produces a truly random value.

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