CODEWITHSUNDEEP
c++
Chicko Bueno
Chicko Bueno

Reputation: 337

How do I generate totally a random number at a time?

I want to create 3 random number at a time (simultaneously). However, they returned me the same numbers at a time even though they are actually random. Example:

------------------------
Variable:   A   B   C
------------------------
Time 1  :   5   5   5
Time 2  :   3   3   3
Time 3  :   9   9   9
------------------------

They suppose to be different numbers at all. From the observation, I can see that my code can only pick a random number at a time (interval 1 second). Here is my generator code that I'm using:

unsigned int CMain::GenerateRandom(int min, int max)
{
    srand((unsigned)time(0)); 
    unsigned int random_integer; 
    int lowest = min, highest = max; 
    int range = (highest - lowest) + 1;

    random_integer = lowest + int(range * rand() / (RAND_MAX + 1.0));

    return random_integer;
}

How could I generate a totally random numbers at a time? Please help.

Thank you.

Upvotes: 1

Views: 4194

Answers (4)

pic11
pic11

Reputation: 14943

time(0) changes slowly. If you query GenerateRandom quickly you can get the same number multiple times.

But in general, that isn't a right way to generate random numbers. You want to seed the random number generator only once, before any other function uses it. Treat rand as a global singleton object. If any of your functions modifies its seed by calling srand, then the change will affect all other calls to rand.

Upvotes: 2

Oscar Gomez
Oscar Gomez

Reputation: 18488

The problem is that you are calling srand() for every iteration. Srand() is setting a seed based on the current timestamp. Therefore you only need to call srand() once, and just call rand() to generate a new pseudo-random number. I say pseudo-random because computers cannot generate truly random numbers.

Sample code:

#include <iostream>
#include <cstdlib>

int main()
{
int i, r;

srand(time(0));

for(i = 0; r <= 20000; i++) 
r = rand();
return 0;
}

Upvotes: 2

Jonathan Wood
Jonathan Wood

Reputation: 67193

Don't call srand() each time you generate a new random number. Call it once at the start of your program and then just call rand() each time you need a new random number.

FYI: Values returned from rand() are not "totally random". They are pseudo-random numbers generated by an algorithm. (This is not related to your question though.)

Upvotes: 3

Mario
Mario

Reputation: 36487

Your issue here is you're resetting the random seed every call using the current time which you shouldn't do.

Call srand() once before querying any random numbers - that's all and more than enough.

Right now you always reset your random seed to the exact same value (as you use current time). Random numbers in PCs aren't really random at all. The same seed will always result in the same set of random numbers generated later on. This is intentional and used in e.g. savegames for games to always have the same things happen without having to save every random number generated, etc.

Upvotes: 10

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