Random Function

[RandomDever]

Is there a way to have a random range function that never repeats any digit?

[dandymcgee]

Use a normal random number generator, but store each generated number somewhere and check against it. If you find a match generate a new number. Dunno if there's a better way.

[MarauderIIC]

Any digit? You mean like
12345
54321 is ok but
10000 is not?

[dandymcgee]

Any digit? You mean like
12345
54321 is ok but
10000 is not?

Wouldn't have thought of it that way.

[RandomDever]

No I mean like if i ran the program:

1
2
3
4
5
6
3
6

(Which is okay )
Then I run it again:

1
2
3
4
5
6
3
6

That's repeating

[Bakkon]

That's because the rand() function picks a number based on how long the program's been running or some such. You need to generate a new seed before using random numbers. Use srand(#) where you feed it in something like timeGetTime() or SDL_GetTicks().

[MarauderIIC]

That's because the rand() function picks a number based on how long the program's been running or some such. You need to generate a new seed before using random numbers. Use srand(#) where you feed it in something like timeGetTime() or SDL_GetTicks().

I usually feed it time() (from #include <ctime>) on the first call to srand and every subsequent seed I use the last result from rand(). I find this tends to give me better non-repetitiveness than just seeding with time() every time. YMMV.
Like this:

Code: Select all

#include <ctime> //time
#include <iostream> //cout
#include <cstdlib> //rand
using namespace std;

int main() {
    srand(time(NULL));
    unsigned int num = rand();
    cout << "Something between 0 and 9: " << num % 10 << endl;
    srand(num);

    return 0;
}

[avansc]

what mar suggested would work and is how i learnt as well. but im not sure what randomization algorithm C uses.
if its anything like a montecarlo based algo its not completely random and will repeat. even to the point where you can predict the numbers.
but in all reality you wont notice it.

[dandymcgee]

what mar suggested would work and is how i learnt as well. but im not sure what randomization algorithm C uses.
if its anything like a montecarlo based algo its not completely random and will repeat. even to the point where you can predict the numbers.
but in all reality you wont notice it.

The most important factor in calculating random sequences is always what you plan to use it for. Top Secret level encryption, or a number guessing game?

[zodiac976]

If you don't want the same random numbers to appear over and
over you need to set a seed first using srand() for instance. If
that is what you're asking.

Use a seed like this... srand(((unsigned int)(time(NULL)));
Also use the <ctime> and <cstdlib> includes.

[avansc]

If you don't want the same random numbers to appear over and
over you need to set a seed first using srand() for instance. If
that is what you're asking.

Use a seed like this... srand((unsigned int)(time(NULL));
Also use the <ctime> and <cstdlib> includes.

do you not read?

[zodiac976]

If you don't want the same random numbers to appear over and
over you need to set a seed first using srand() for instance. If
that is what you're asking.

Use a seed like this... srand((unsigned int)(time(NULL));
Also use the <ctime> and <cstdlib> includes.

do you not read?

What are you talking about?

[avansc]

you basically just dumped the same thing that was already posted by someone else.

[zodiac976]

you basically just dumped the same thing that was already posted by someone else.

srand(((unsigned int)(time(NULL)));
//for integers
int randNum = rand() % 100;
//for precision numbers
randNum = (randNum / 100) + rand() % 100;

Almost the same but not exactly

[avansc]

thats what you call spin. you should be in politics.