Returning values from a function

[Materialised]

I am writing a simple function to initialise 3 variables to pesudo
random numbers.

I have a function which is as follows

int randomise( int x, int y, intz)
{
srand((unsigned )time(NULL));
x = rand();
y = rand();
z = rand();

}
And I call this function with

randomise(a,b,c );

However a,b,c do not contain the randomised integers, I understand this
is a problem with the return value of my function,
I have tried
return x,y,z;
But this doesnt work either.

Can anyone point out where my problem is?

[WW]

Materialised wrote:

I am writing a simple function to initialise 3 variables to pesudo
random numbers.

I have a function which is as follows

int randomise( int x, int y, intz)
{
srand((unsigned )time(NULL));
x = rand();
y = rand();
z = rand();

}
And I call this function with

randomise(a,b,c );

However a,b,c do not contain the randomised integers, I understand
this is a problem with the return value of my function,
I have tried
return x,y,z;
But this doesnt work either.

Can anyone point out where my problem is?

Ehem. The first one is that you try to program in C++ without a good
textbook. :-(

First of all, your program has not return value. You do not return
anything. There is no return statement.

The second: how do you expect to return 3 integers in one?

The third: as you wrote the function definition (signature) it takes the
arguments by value, so x,y and z (which you have clearly typed wrong) is a
*copy* of a b and c. Writing into them will write into the copy.

You can take the arguments by reference, then you will be able to change
them. *If* you work in C++. If you do work in C, you will need to take
pointers to them.

--
WW aka Attila

[Eric Sosman]

Materialised wrote:

I am writing a simple function to initialise 3 variables to pesudo
random numbers.

I have a function which is as follows

int randomise( int x, int y, intz)
{
srand((unsigned )time(NULL));
x = rand();
y = rand();
z = rand();

}
And I call this function with

randomise(a,b,c );

However a,b,c do not contain the randomised integers, I understand this
is a problem with the return value of my function,
I have tried
return x,y,z;
But this doesnt work either.

Can anyone point out where my problem is?

These are Questions 4.8 and 20.1 in the comp.lang.c
Frequently Asked Questions (FAQ) list

http://www.eskimo.com/~scs/C-faq/top.html

--
Er*********@sun .com

[Martin Ambuhl]

Materialised wrote:

I am writing a simple function to initialise 3 variables to pesudo
random numbers.

I have a function which is as follows

int randomise( int x, int y, intz)
{
srand((unsigned )time(NULL));
x = rand();
y = rand();
z = rand();

}
And I call this function with

randomise(a,b,c );

However a,b,c do not contain the randomised integers, I understand this
is a problem with the return value of my function,
I have tried
return x,y,z;
But this doesnt work either.

Can anyone point out where my problem is?

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

void randomise(int *x, int *y, int *z)
{
srand((unsigned ) time(NULL));
*x = rand();
*y = rand();
*z = rand();
}

int main(void)
{
int a, b, c;
randomise(&a, &b, &c);
printf("%d %d %d\n", a, b, c);
return 0;
}

--
Martin Ambuhl

[Materialised]

WW wrote:

Materialised wrote:

I am writing a simple function to initialise 3 variables to pesudo
random numbers.

I have a function which is as follows

int randomise( int x, int y, intz)
{
srand((unsign ed)time(NULL));
x = rand();
y = rand();
z = rand();

}
And I call this function with

randomise(a,b ,c);

However a,b,c do not contain the randomised integers, I understand
this is a problem with the return value of my function,
I have tried
return x,y,z;
But this doesnt work either.

Can anyone point out where my problem is?

Ehem. The first one is that you try to program in C++ without a good
textbook. :-(

First of all, your program has not return value. You do not return
anything. There is no return statement.

The second: how do you expect to return 3 integers in one?

The third: as you wrote the function definition (signature) it takes the
arguments by value, so x,y and z (which you have clearly typed wrong) is a
*copy* of a b and c. Writing into them will write into the copy.

You can take the arguments by reference, then you will be able to change
them. *If* you work in C++. If you do work in C, you will need to take
pointers to them.

Thanks for your help, I realised my error right after posting

int randomise()
{
int x;
srand((unsigned )time(NULL));
x = rand();
return x;
}

and in main

a = randomise();
b = randomise();
c = randomise();

[Artie Gold]

Materialised wrote:

WW wrote:

Materialised wrote:

I am writing a simple function to initialise 3 variables to pesudo
random numbers.

I have a function which is as follows

int randomise( int x, int y, intz)
{
srand((unsigned )time(NULL));
x = rand();
y = rand();
z = rand();

}
And I call this function with

randomise(a,b,c );

However a,b,c do not contain the randomised integers, I understand
this is a problem with the return value of my function,
I have tried
return x,y,z;
But this doesnt work either.

Can anyone point out where my problem is?

Ehem. The first one is that you try to program in C++ without a good
textbook. :-(

First of all, your program has not return value. You do not return
anything. There is no return statement.

The second: how do you expect to return 3 integers in one?

The third: as you wrote the function definition (signature) it takes the
arguments by value, so x,y and z (which you have clearly typed wrong) is a
*copy* of a b and c. Writing into them will write into the copy.

You can take the arguments by reference, then you will be able to change
them. *If* you work in C++. If you do work in C, you will need to take
pointers to them.

Thanks for your help, I realised my error right after posting

int randomise()
{
int x;
srand((unsigned )time(NULL));
x = rand();
return x;
}

and in main

a = randomise();
b = randomise();
c = randomise();

No, you don't want to do that either.
Calling `srand()' multiple times like that (i.e. for each call to
`rand()') will not make the numbers any more random, and may do
exactly the opposite.

Call srand() once...

....and please reread the suggestions elsethread.

HTH,
--ag

--
Artie Gold -- Austin, Texas
Oh, for the good old days of regular old SPAM.

[Dan Pop]

In <bn************ @ID-204621.news.uni-berlin.de> Materialised <ma**********@p rivacy.net> writes:

I am writing a simple function to initialise 3 variables to pesudo
random numbers.

I have a function which is as follows

int randomise( int x, int y, intz)
{
srand((unsigne d)time(NULL));
x = rand();
y = rand();
z = rand();

}
And I call this function with

randomise(a,b, c);

However a,b,c do not contain the randomised integers, I understand this
is a problem with the return value of my function,
I have tried
return x,y,z;
But this doesnt work either.

Can anyone point out where my problem is?

Sure, both your favourite C book and the FAQ can.

The *right* way of solving this problem in C is by using a structure:

struct random { int x, y, z; };

struct random randomise(void)
{
struct random t;
srand((unsigned )time(NULL)); /* this function call doesn't belong
here, unless you call this function exactly once */
t.x = rand();
t.y = rand();
t.z = rand();
return t;
}

Ignore any advice recommending the usage of three pointers in the
function's interface. Such interfaces are evil, in general, even if, in
this particular case, there is no big deal. Functions should not use
their parameters as a way of returning back information to the caller.

Dan
--
Dan Pop
DESY Zeuthen, RZ group
Email: Da*****@ifh.de

[Christopher Benson-Manica]

In comp.lang.c Dan Pop <Da*****@cern.c h> wrote:

Ignore any advice recommending the usage of three pointers in the
function's interface. Such interfaces are evil, in general, even if, in
this particular case, there is no big deal. Functions should not use
their parameters as a way of returning back information to the caller.

Why is this? In what circumstances can pointers lead to tragedy?

--
Christopher Benson-Manica | I *should* know what I'm talking about - if I
ataru(at)cybers pace.org | don't, I need to know. Flames welcome.

[Default User]

WW wrote:

You can take the arguments by reference, then you will be able to change
them. *If* you work in C++. If you do work in C, you will need to take
pointers to them.

Where did the OP say he was working in C++?


Brian Rodenborn

[Default User]

WW wrote:

Ehem. The first one is that you try to program in C++ without a good
textbook. :-(

C++