WHy my program doesn't work

[Duardo Mattheo]

#include<iostream.h>
#include<stdlib.h>
void main(void)
{
unsigned int u=int(1 000 000 000*rand()%RAND_MAX);
cout<<"Money summed = "<<(u);
}

thank you,
Duardo

 

[Bo Persson]

Duardo Mattheo wrote:
:: #include<iostream.h>
:: #include<stdlib.h>
:: void main(void)
:: {
:: unsigned int u=int(1 000 000 000*rand()%RAND_MAX);
:: cout<<"Money summed = "<<(u);
:: }
::
:: thank you,
:: Duardo

Depending on the machine you have, 1 billion times some value is highly
likely to be larger than what an unsigned int can store.


Bo Persson

 

[Colander]

#include<iostream.h>
#include<stdlib.h>
void main(void)
{
unsigned int u=int(1 000 000 000*rand()%RAND_MAX);
cout<<"Money summed = "<<(u);

}

thank you,
Duardo

Because you have to write

'std::cout' where you wrote 'cout'.

Because you can't write a number with spaces in it.

Because main has to return int.

So the next will work:
#include<iostream>
#include<stdlib.h>
int main(void)
{
unsigned int u=int(1000000000*rand()%RAND_MAX);
std::cout<<"Money summed = "<<(u);

return 0;
}

 

[Colander]

Because you have to write

'std::cout' where you wrote 'cout'.

Because you can't write a number with spaces in it.

Because main has to return int.

So the next will work:
#include<iostream>
#include<stdlib.h>
int main(void)
{
unsigned int u=int(1000000000*rand()%RAND_MAX);
std::cout<<"Money summed = "<<(u);

return 0;

}

(Replying to one selfs, what does the world do to me)

Now that we have the systax right, we can look at wat you are trying
to do.

I guess you want a random number between 0 or 1 and 1000000000.

This is not what the programme does....

Please lookup srand and rand in your manual.

srand is a function that will give you a new/different random number
each time you run your progrogramme.

Doing a modulo operation makes sure that a number is in a range, in
your case the range will be [0, RAND_MAX), and not [0, 1000000000).

Good luck

 

[=?ISO-8859-1?Q?Erik_Wikstr=F6m?=]

Because you have to write

'std::cout' where you wrote 'cout'.

Because you can't write a number with spaces in it.

Because main has to return int.

So the next will work:
#include<iostream>
#include<stdlib.h>
int main(void)
{
unsigned int u=int(1000000000*rand()%RAND_MAX);
std::cout<<"Money summed = "<<(u);

return 0;

}

(Replying to one selfs, what does the world do to me)

Now that we have the systax right, we can look at wat you are trying
to do.

I guess you want a random number between 0 or 1 and 1000000000.

This is not what the programme does....

Please lookup srand and rand in your manual.

srand is a function that will give you a new/different random number
each time you run your progrogramme.

Doing a modulo operation makes sure that a number is in a range, in
your case the range will be [0, RAND_MAX), and not [0, 1000000000).

And I'd like to point out that the range of the values output by rand
already is [0, RAND_MAX], after all that is what RAND_MAX means, the max
number that rand can output. So the modulo (%) operator is not needed.
Perhaps a / was intended so that the value will be between 0 and 1000000000?

Notice also that you need to seed rand before usage, or there's a great
chance that it will return the same value each time you run the
application, you can use the current time to get a quite good (but not
cryptographically secure) seed:

#include <iostream>
#include <cstdlib>
#include <ctime>

int main()
{
srand(time(0));
unsigned int nr = static_cast<unsigned int>(1000000000 *
rand() / double(RAND_MAX)
);
std::cout << nr;
return 0;
}

 

[=?ISO-8859-1?Q?Erik_Wikstr=F6m?=]

Duardo Mattheo wrote:
:: #include<iostream.h>
:: #include<stdlib.h>
:: void main(void)
:: {
:: unsigned int u=int(1 000 000 000*rand()%RAND_MAX);
:: cout<<"Money summed = "<<(u);
:: }
::
:: thank you,
:: Duardo

Depending on the machine you have, 1 billion times some value is highly
likely to be larger than what an unsigned int can store.

It will probably be enough on a modern 32-bit machine. What the OP
should watch out for is the fact that he/she is casting the result to
int but assigning to an unsigned int.

 

[SasQ]

Dnia Sat, 24 Mar 2007 05:30:55 -0700, Colander napisa³(a):

#include<stdlib.h>

std::cout<<"Money summed = "<<(u);

Why 'u' in parenthesis?

 

[Adrian Hawryluk]

#include <iostream>
#include <cstdlib>
#include <ctime>

int main()
{
srand(time(0));
unsigned int nr = static_cast<unsigned int>(1000000000 *
rand() / double(RAND_MAX)

I don't think that will work. Assuming that the largest value is about
4Gib, you will overflow most of the data that rand() outputs when
multiplying it by 1000000000, loosing most of your resolution. The
following should work:

unsigned int nr = static_cast<unsigned int>(
(rand() * rand()) % 1000000000)

Assuming that RAND_MAX*RAND_MAX >= 1000000000-1 (in actual math, not on
a CPU's integer arithmetic set) this should work. And although (rand()
* rand()) could overflow, it wouldn't matter as that information is not
needed when trying to get a value in the range [0, 1000000000).

);
std::cout << nr;
return 0;
}

Adrian
--
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[=?ISO-8859-1?Q?Erik_Wikstr=F6m?=]

I don't think that will work. Assuming that the largest value is about
4Gib, you will overflow most of the data that rand() outputs when
multiplying it by 1000000000, loosing most of your resolution. The
following should work:

unsigned int nr = static_cast<unsigned int>(
(rand() * rand()) % 1000000000)

I was more thinking along the lines of this (notice the added parentheses):
unsigned int nr = static_cast<unsigned int>(1000000000 *
(rand() / double(RAND_MAX))

It will not be able to produce all values in the range 0-1000000000, but
then again, with that range who would notice