Random Numbers...Problem With FAQ Answer

Hi all,

I've just tried testing the random numbers answer in the FAQ (http://faq.cprogramming.com/cgi-bin/...&id=1043284385) and it isn't working for me. I've got the exact same C++ code shown there:

Code:

---

#include <iostream>
#include <ctime>

int main(void)
{
  int i, r;

  for (i = 0; i < 20; i++)
  {
    r = GetRand(10, 12);
    std::cout <<"Your number is " <<r <<std::endl;
  }

  return(0);
}

---

All that happens is that line ten is highlighted, with the error "'GetRand' undeclared (first use this function)".

It's probably a real simple answer, but I've just started learning C++, so could anybody be kind enough to help?

Thanks very much,
Mike

Try using the <cstdlib> header file .
I only know srand so i could be wrong.
And your return 0; is mistake also.
take away the () sourounding the 0;

Hmm... still gives the same error message, thanks anyway blackgold :)

Anyone got any ideas?

Thanks a lot,
Mike

They just showed you what needed to change. You still need the function declaration from the C-code.

>still gives the same error message
Is that all of the code in your program? If so, it's no surprise that the function isn't found as you don't define it. Your code should look something like this:

Code:

---

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

int GetRand(int min, int max);

int main(void)
{
  int i, r;

  for (i = 0; i < 20; i++)
  {
    r = GetRand(10, 12);
    std::cout <<"Your number is " <<r <<std::endl;
  }

  return(0);
}

int GetRand(int min, int max)
{
  static int Init = 0;
  int rc;
 
  if (Init == 0)
  {
    /*
    *  As Init is static, it will remember it's value between
    *  function calls.  We only want srand() run once, so this
    *  is a simple way to ensure that happens.
    */
    std::srand(std::time(NULL));
    Init = 1;
  }

  /*
  * Formula: 
  *    rand() % N  <- To get a number between 0 - N-1
  *    Then add the result to min, giving you
  *    a random number between min - max.
  */ 
  rc = (std::rand() % (max - min + 1) + min);
 
  return (rc);
}

---

>And your return 0; is mistake also.
No it isn't. You can enclose an expression with parentheses, they don't do anything in this case and are perfectly legal.

You can leave () around the 0 on return, its prefectly fine.

Quote:

---

All that happens is that line ten is highlighted, with the error "'GetRand' undeclared (first use this function)".

---

Did you remember to copy GetRand from the example above it?

The example you copied was just showing how to change it to a c++ document.

Code:

---

int GetRand(int min, int max)
{
  static int Init = 0;
  int rc;
 
  if (Init == 0)
  {
    /*
    *  As Init is static, it will remember it's value between
    *  function calls.  We only want srand() run once, so this
    *  is a simple way to ensure that happens.
    */
    srand(time(NULL));
    Init = 1;
  }

  /*
  * Formula: 
  *    rand() % N  <- To get a number between 0 - N-1
  *    Then add the result to min, giving you
  *    a random number between min - max.
  */ 
  rc = (rand() % (max - min + 1) + min);
 
  return (rc);
}

---

Edit: Foiled!

Oh thanks also for the () around ;0 what is the purpose of doing this i wonder?
Thanks alot.

>what is the purpose of doing this i wonder?
Ancient C used to require them, but not for long. The people that learned C at the time continued to use them out of habit, and created confusion. These days it's pretty well known that parentheses aren't required for a return statement, but some people still use it as a matter of style. They feel that it keeps their syntax more consistent.

>They feel that it keeps their syntax more consistent.
Yep. Them old people go through a lot of trouble to stay regular.

Ok thanks alot ,old folks :)

>Them old people go through a lot of trouble to stay regular.
What an awful pun. I wish I'd thought of it. :p

I guess I'll take that as a compliment...

Yup works now. Said it would be something simple :)

Thanks guys.