That's a very insightful question! While it might seem like calling srand() more often would make things "more random," it actually does the opposite. Here is why:
1. Computers are too fast
time(NULL) returns the current time in seconds. A computer can execute the code inside a loop thousands of times in a single second.
If you put srand(time(NULL)) inside a loop:
- Every time the loop repeats within the same second, you are resetting the seed to the exact same value.
- When you reset the seed to the same value,
rand()is forced to restart the sequence from the same starting point. - As a result,
rand()will return the same "random" number over and over again until the clock finally ticks to the next second.
2. Predictability
The goal of a random number generator is to provide a long, unpredictable sequence. By calling srand() multiple times, you are "interrupting" that sequence.
Think of srand() like picking a page in a giant book of random numbers:
- Correct way: You pick a page once (
srand) and then read the numbers one by one (rand). - Incorrect way: Every time you need a number, you flip back to the same page. You'll just keep reading the first number on that page!
Practical Example
If you did this:
for (int i = 0; i < 5; i++) {
srand(time(NULL)); // Resetting seed every time
printf("%d ", rand() % 10);
}The output would likely look like this: 3 3 3 3 3 (because the time didn't change between loops).
Rule of Thumb
You should call srand() exactly once at the very beginning of your program (usually at the top of main). This "seeds" the generator once, allowing rand() to produce a smooth, varying sequence for the rest of the program's life.
