Generating same random numbers...

[teocl5]

Hi all,

I have been trying to figure out this matter for hours. I have a code that generates random numbers. Regardless of how many times i compiled and run, i still get the same random numbers. Anyone care to explain?

int a;
for (int i=0; i < 5; i++)
{
   a = rand();
   cout << a << endl;
}

1804289383
846930886
1681692777
1714636915
1957747793

[Gaminic]

C++'s built-in RNG doesn't seed itself. ("What's a seed?" Well, it's impossible for a computer to generate a random number without random input. It requires (a) seed(s) to randomize.)

You can manually seed the RNG using srand(uint). http://www.cplusplus.com/reference/clibrary/cstdlib/srand/

It's quite custom to use the current time as a seed. With sufficient precision on your time() function, it's pretty random. The link uses time in its example, so might as well just copypaste!

(P.S.: It's often very handy to use a constant to seed your RNG. That way, you can mimic a random without stochasticity if, for example, you need to compare outcomes of several runtimes.)

[whitenite1]

Because the numbers that are being called, all start at the same place in memory. To get different values, you have to seed the rand function.The best way is to #include <time.h> , then at the top of your program, after main(),

 time_t t;
srand((unsigned) time(&t));

. You will get a different set of numbers each time you run your program.

[teocl5]

Thank you Gaminic & whitenite1! I am enlightened now. Thanks for the help rendered!