how to generate a random number

[DavidOliveira]

i wanna generate random numbers with no repeats, i have this code

#include <cstdlib>
#include <iostream>
using namespace std;
int main()
{
int randomNumber;
for(int i = 0; i < 15
; i++) //print random #s 15 times
{randomNumber = (rand() % 25) + 1;
cout << randomNumber << endl;getchar(
);
}
return 0;
}

but it generate the same sequence 17-18-10-1-20-25-4-9-13-15-6-21-7-3-12 everytime

how can i fix it

[Kripton]

Try:

#include <cstdlib> 
#include <ctime> 
#include <iostream>using namespace std;int main() 
{ 
	srand((unsigned)time(0)); 
	int random_integer = rand(); 
	cout << random_integer << endl; 
}

In most coding languages the random number call will produce the same numbers everytime. We use the time as a seed value and generate the numbers from that

Edited July 7, 2009 by Kripton

[GamingMasteR]

Use time functions - like 'GetTickCount' - and mix results to get random numbers .

[DavidOliveira]

Use time functions - like 'GetTickCount' - and mix results to get random numbers .

how i dont know this function could give a example

[Bleed]

check this out: http://www.cplusplus.com/reference/clibrary/cstdlib/rand/

Use time functions - like 'GetTickCount' - and mix results to get random numbers .

The GetTickCount function retrieves the number of milliseconds that have elapsed since Windows was started. It does not do random stuff.

how i dont know this function could give a example

using GetTickCount requires knowledge in win32 API programming. try google one of those.

Edited July 7, 2009 by Lumiliyab

[GamingMasteR]

The GetTickCount function retrieves the number of milliseconds that have elapsed since Windows was started. It does not do random stuff.

And this elapsed time is random by itself, you can get the same value from GetTickCount more than one time rarely .

[DavidOliveira]

check this out: <a href="http://www.cplusplus.com/reference/clibrary/cstdlib/rand/" target="_blank">http://www.cplusplus.com/reference/clibrary/cstdlib/rand/</a>

Use time functions - like 'GetTickCount' - and mix results to get random numbers .

The GetTickCount function retrieves the number of milliseconds that have elapsed since Windows was started. It does not do random stuff.

how i dont know this function could give a example

using GetTickCount requires knowledge in win32 API programming. try google one of those.

thanks man i fix it!!!

[atom0s]

Kripton answered your question already. Because you are using rand() you need to call srand() with a dynamic seed to allow rand() calls to actually be random.

Using timestamps, such as a unix timestamp, for your seed with other math involved is probably your best bet to have a unique seed as well as timestamps do not repeat in that manner.