time()

**Thad Smith** · Jun 27 '08, 07:32 PM

Re: time()

Bill Cunningham wrote:

I have no idea what to do with time () or another function to change the
time_t data type to int to get numbers say from 0-20 that are ints.

What units do you want? gmtime() will convert time_t into struct tm
fields. Standard C doesn't define the encoding of time_t values.

time()
reports a huge number of seconds

maybe

and when using rand() truely produce a fake
randomness.

A pseudo random numbergenerator does not generate true random values.

I want smaller numbers.

Take 0 -- it's a small number. If that isn't sufficient, define your
requirements more precisely.

We have functions like strtod and strtol

to change chars into doubles or longs why not change time_t to int?

gmtime() and localtime() do that.

--
Thad

**Keith Thompson** · Jun 27 '08, 07:32 PM

Re: time()

"Bill Cunningham" <nospam@nspam.c omwrites:

I have no idea what to do with time () or another function to change the
time_t data type to int to get numbers say from 0-20 that are ints.

What for? If you want numbers in the range 0-20, what does that have
to do with time()?

time()
reports a huge number of seconds and when using rand() truely produce a fake
randomness.

I don't know what you mean by that. You're using time() and rand()
together somehow? How exactly? Presumably srand() is involved
somehow, but you didn't mention it.

I want smaller numbers. We have functions like strtod and strtol
to change chars into doubles or longs why not change time_t to int?

time_t is an arithmetic type capable of representing times. That's
*all* the standard tells you about it. You can convert a time_t value
to int the same way you'd convert any numeric type to another one
(just assign it), but that's not a useful thing to do; for one thing,
the result of time() may or may not fit within the range of int.

Let's back off a bit. You're trying to accomplish something, but you
haven't actually told us exactly what it is. Instead, you've thrown
together a few things that you might *use* to accomplish something
(time(), type time_t, type int, numbers in the range 0-20, rand(),
"smaller numbers") -- things that apparently aren't doing what you
want them to do.

It's like asking "Should I use a hammer or a screwdriver? What about
a staple gun?" without saying what you're trying to build.

First, tell us *exactly* what you want to accomplish. State your
problem without referring to any possible solution or piece of a
solution.

Then, *separately*, you might ask whether some proposed solution, or
something like it, will do what you want. If you can express the
proposed solution in C code, even if it doesn't work or is incorrect,
that's great. But we can't help without knowing what you're trying to
do.

Have you read <http://www.catb.org/~esr/faqs/smart-questions.html> ?

You might also take a look at section 13 in the comp.lang.c FAQ,
particularly the questions on random numbers.

--
Keith Thompson (The_Other_Keit h) <kst-u@mib.org>
Nokia
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"

**Bill Cunningham** · Jun 27 '08, 07:32 PM

Re: time()

[snip]

We have functions like strtod and strtol

>to change chars into doubles or longs why not change time_t to int?

>
gmtime() and localtime() do that.
>

OK Thad I'll try that. THanks.

Bill

**Bill Cunningham** · Jun 27 '08, 07:33 PM

Re: time()

[snip]

Let's back off a bit. You're trying to accomplish something, but you
haven't actually told us exactly what it is. Instead, you've thrown
together a few things that you might *use* to accomplish something
(time(), type time_t, type int, numbers in the range 0-20, rand(),
"smaller numbers") -- things that apparently aren't doing what you
want them to do.
>
It's like asking "Should I use a hammer or a screwdriver? What about
a staple gun?" without saying what you're trying to build.
>
First, tell us *exactly* what you want to accomplish. State your
problem without referring to any possible solution or piece of a
solution.
>
Then, *separately*, you might ask whether some proposed solution, or
something like it, will do what you want. If you can express the
proposed solution in C code, even if it doesn't work or is incorrect,
that's great. But we can't help without knowing what you're trying to
do.

Say you have two dice of six sides. Can you use rand() to create 12
options by rolling the die. Now there's another way you can do this simply
but using arrays but I do not know how. Something like this.

int a [12];

Ok there's 12 objects or

int a [20];

like I want. I can use for to loop over them but I can't get randomness.
That's a feature I do not know how to reproduce. It will have to someway
depend on the system and most use the system time.

Bill

**Gordon Burditt** · Jun 27 '08, 07:33 PM

Re: time()

I have no idea what to do with time () or another function to change the

>time_t data type to int to get numbers say from 0-20 that are ints. time()

What does the time have to do with the ints? Do you live on a
planet where there are 20 hours in a day?

If you want to convert the time to human-readable form (month, day,
year, hour, minute, second) use localtime(), although none of those
numbers run from 0-20 inclusive without also including some outside
that range.

>reports a huge number of seconds and when using rand() truely produce a fake
>randomness. I want smaller numbers.

If you are trying to use time() as a pseudo-random seed generator
to get fake randomness, consider what the % operator does. What
number range might time() % 21 produce? What might happen if you
use it twice in the same second?

>We have functions like strtod and strtol
>to change chars into doubles or longs why not change time_t to int?

time_t *is* an integer type, although it need not represent a "number
of <time unitsince <epoch>". It might not fit in an int.

**Gordon Burditt** · Jun 27 '08, 07:33 PM

Re: time()

Say you have two dice of six sides. Can you use rand() to create 12

>options by rolling the die.

Note that rolling two dice of six sides each (adding the results)
and rolling one die of 12 sides does NOT generate the same probability
distribution.

>Now there's another way you can do this simply
>but using arrays but I do not know how. Something like this.
>
>int a [12];
>
>Ok there's 12 objects or
>
>int a [20];
>
>like I want. I can use for to loop over them but I can't get randomness.

Ok, you can use an array of N elements to translate from a number from
0 .. N-1 to something you want, where a[3] might be the code for the
"+1 sword of troll slaying".

Computers do not generate *real* random numbers without hardware
support. Common ways of getting random numbers include measuring
radioactive decay, measuring thermal noise, or fine-grained typing
of manual events like keystrokes.

>That's a feature I do not know how to reproduce. It will have to someway
>depend on the system and most use the system time.

Note that if you use pseudo-random numbers to implement casino games
and let the public play these games, betting REAL money, you're going
to lose your shirt.

Something like rand() % 21 will generate numbers from 0 .. 20, inclusive,
but the distribution will not be exactly even since 21 does not divide
RAND_MAX+1 evenly.

Seeding rand() is often done with the system time, like:

srand((unsigned ) time() );

**Bill Cunningham** · Jun 27 '08, 07:33 PM

Re: time()

[snip]

Note that if you use pseudo-random numbers to implement casino games
and let the public play these games, betting REAL money, you're going
to lose your shirt.
>
Something like rand() % 21 will generate numbers from 0 .. 20, inclusive,
but the distribution will not be exactly even since 21 does not divide
RAND_MAX+1 evenly.
>
Seeding rand() is often done with the system time, like:
>
srand((unsigned ) time() );

I want to create a utility for playing online game like RPGs. So I was
wanting to write a "dice rolling" utility. That's exactly what I am wanting.

Bill

**Keith Thompson** · Jun 27 '08, 07:33 PM

Re: time()

"Bill Cunningham" <nospam@nspam.c omwrites:

[snip]
>

>Let's back off a bit. You're trying to accomplish something, but you
>haven't actually told us exactly what it is. Instead, you've thrown
>together a few things that you might *use* to accomplish something
>(time(), type time_t, type int, numbers in the range 0-20, rand(),
>"smaller numbers") -- things that apparently aren't doing what you
>want them to do.
>>
>It's like asking "Should I use a hammer or a screwdriver? What about
>a staple gun?" without saying what you're trying to build.
>>
>First, tell us *exactly* what you want to accomplish. State your
>problem without referring to any possible solution or piece of a
>solution.
>>
>Then, *separately*, you might ask whether some proposed solution, or
>something like it, will do what you want. If you can express the
>proposed solution in C code, even if it doesn't work or is incorrect,
>that's great. But we can't help without knowing what you're trying to
>do.

I wrote the above. When you posted your followup, your newsreader
should have provided an attribution line, something like

Keith Thompson <kst-u@mib.orgwrites :

Please leave that line in place. Quoting somebody without attribution
is considered rude. (I think I've told you this before.)

Say you have two dice of six sides. Can you use rand() to create 12
options by rolling the die. Now there's another way you can do this simply
but using arrays but I do not know how. Something like this.
>
int a [12];
>
Ok there's 12 objects or
>
int a [20];
>
like I want. I can use for to loop over them but I can't get randomness.
That's a feature I do not know how to reproduce. It will have to someway
depend on the system and most use the system time.

You're still not making sense.

If I roll two six-sided dice, there are 36 (6*6) possible outcomes,
not 12. I suppose you could divide these up into 12 sets of 3
outcomes each, but I suspect that's not what you had in mind.

You stated your problem extremely vaguely, and mixed it with a
mishmash of possible pieces of a solution (rand(), a 12-element or
20-element array, a for loop, the system time). That's exactly what I
asked you not to do.

Please start by stating the problem you're trying to solve *without*
reference to the method used to solve it. Don't talk about rand(), or
time_t, or time(). Tell us what result you're trying to achieve. You
should be able to do that in one sentence or one short paragraph.

An example:

I want to generate a sequence of 73 uniformly distributed random
numbers, each in the range 37 to 153. I want the sequence to be
different each time I run my program.

(I've deliberately written something that differs from what you seem
to be looking for. You need to tell us what you want.)

Once you've done that, and *only* after you've done that, you can ask
whether certain tools (rand(), time(), a for loop) might or might not
be part of a solution.

--
Keith Thompson (The_Other_Keit h) <kst-u@mib.org>
Nokia
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"

**Keith Thompson** · Jun 27 '08, 07:33 PM

Re: time()

gordonb.3jhcg@b urditt.org (Gordon Burditt) writes:
[...]

time_t *is* an integer type, although it need not represent a "number
of <time unitsince <epoch>". It might not fit in an int.

time_t is an integer type on most implementations . The standard only
guarantees that it's an arithmetic type capable of representing times.
It could be floating-point. (It could even, in a sufficiently
perverse implementation, be complex or imaginary.)

(I do not give permission to quote this article, or any other article
I post to Usenet, without attribution.)

--
Keith Thompson (The_Other_Keit h) <kst-u@mib.org>
Nokia
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"

**Bill Cunningham** · Jun 27 '08, 07:33 PM

Re: time()

"Keith Thompson" <kst-u@mib.orgwrote in message
news:87lk2zj8ae .fsf@kvetch.smo v.org...

I wrote the above. When you posted your followup, your newsreader
should have provided an attribution line, something like
>
Keith Thompson <kst-u@mib.orgwrites :
>
Please leave that line in place. Quoting somebody without attribution
is considered rude. (I think I've told you this before.)

Now is this how it should be. I'm using outlook express :( It took me
awhile way way back to learn not to top post. Sorry I will work on this. I
have to do it all manually.

Bill

**Bill Cunningham** · Jun 27 '08, 07:33 PM

Re: time()

"Keith Thompson" <kst-u@mib.orgwrote in message
news:87hcdnj7p4 .fsf@kvetch.smo v.org...

(I do not give permission to quote this article, or any other article
I post to Usenet, without attribution.)
>

What do you mean by this Keith? Do you not want to be quoted in clc's
message threads?

Bill

**Bartc** · Jun 27 '08, 07:33 PM

Re: time()

"Keith Thompson" <kst-u@mib.orgwrote in message
news:87lk2zj8ae .fsf@kvetch.smo v.org...

"Bill Cunningham" <nospam@nspam.c omwrites:

>[snip]
> Say you have two dice of six sides. Can you use rand() to create 12
>options by rolling the die. Now there's another way you can do this
>simply
>but using arrays but I do not know how. Something like this.
>>
>int a [12];
>>
>Ok there's 12 objects or
>>
>int a [20];
>>
>like I want. I can use for to loop over them but I can't get randomness.
>That's a feature I do not know how to reproduce. It will have to someway
>depend on the system and most use the system time.

>
You're still not making sense.
>
If I roll two six-sided dice, there are 36 (6*6) possible outcomes,
not 12. I suppose you could divide these up into 12 sets of 3
outcomes each, but I suspect that's not what you had in mind.

I make it only 11 outcomes (1+1 to 6+6). Although if you listed all
combinations there would be 36.

If certain combinations are important, then you can list the 6 outcomes for
each die separately, totalling 12 outcomes.

--
Bartc

**pete** · Jun 27 '08, 07:33 PM

Re: time()

Bill Cunningham wrote:

I want to create a utility for playing online game like RPGs. So I was
wanting to write a "dice rolling" utility. That's exactly what I am wanting.

/* BEGIN dice.c */

#include <stdio.h>
#include <stdlib.h>

#define THROWS 1000
#define str(s) # s
#define xstr(s) str(s)

int main(void)
{
int sum[13] = {0};
unsigned count = THROWS;

while (count-- != 0) {
++sum[rand() % 6 + 1 + rand() % 6 + 1];
}
puts("Dice totals from "xstr(THROW S)" throws of a pair of dice:");
puts("value count");
for (count = 0; count != sizeof sum / sizeof *sum; ++count) {
printf("%2u %2d\n", count, sum[count]);
}
return 0;
}

/* END dice.c */

--
pete

**Bill Cunningham** · Jun 27 '08, 07:33 PM

Re: time()

"pete" <pfiland@mindsp ring.comwrote in message
news:wsednTuJDI MHgIjVnZ2dnUVZ_ gSdnZ2d@earthli nk.com...

>
/* BEGIN dice.c */
>
#include <stdio.h>
#include <stdlib.h>
>
#define THROWS 1000
#define str(s) # s
#define xstr(s) str(s)
>
int main(void)
{
int sum[13] = {0};
unsigned count = THROWS;
>
while (count-- != 0) {
++sum[rand() % 6 + 1 + rand() % 6 + 1];
}
puts("Dice totals from "xstr(THROW S)" throws of a pair of dice:");
puts("value count");
for (count = 0; count != sizeof sum / sizeof *sum; ++count) {
printf("%2u %2d\n", count, sum[count]);
}
return 0;
}
>
/* END dice.c */
>

Thanks Pete but I can't read some of the program. What does int sum
[13]={0}; mean? Why is there a zero in parenthesis? Also
#define str(s) # s

#define xstr(s) str(s)

What does that code do?

The rest I can pretty much make out. But what does the % after rand mean?

This is how to learn C.

Bill

time()

time()

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