Random Numbers

[Astronouth7303]

Anybody know how to Generate a random number?

If you check the pdfs that came with the compiler (CD:\mcc18\doc\MPLAB-C18-Libraries.pdf), there is a random number type thing, but I can't use it!

Here:

//Prototype
int rand(void);

//...

/****************************************
* FUNCTION NAME: Random
* PURPOSE: Returns a random char
* CALLED FROM: Where ever
* ARGUMENTS: none
* RETURNS: unsigned char
****************************************/
unsigned char Random(void)
{
unsigned int rnd;

rnd = Rand;

rnd = rnd / RAND_MAX;
return (unsigned char) (rnd & 0xFF);
}

The thing is, When I build, I get
...\user_routines.c:267:Error [1105] symbol 'Rand' has not been defined

Help?!?

[Dave Flowerday]

You might want to try

rnd = rand();

And make sure you include stdlib.h in your user_routines.c file.

[Astronouth7303]

Originally Posted by Dave Flowerday

You might want to try

rnd = rand();

And make sure you include stdlib.h in your user_routines.c file.

Ok, I tried that. Get this: ...\user_routines.c:267:Warning [2058] call of function without prototype:

unsigned char Random(void)
{
  unsigned int rnd;
//  Right Here! ************************
  rnd = Rand();
  
  rnd = rnd / RAND_MAX;
  return (unsigned char) (rnd & 0xFF);
}

And I included Std.lib.: #include <stdlib.h>


Other Half: ...\user_routines.c:289:Error [1131] type mismatch in assignment:

void Default_Routine(void)
{ 

//...

//Between Here...
pwm01=pwm03=Random;
pwm02=pwm04=Random;
//... And Here.

//...  
}

P.S.- Tell me if it's some simple Syntax stuff. I'm still trying to get the hang of it.

[Dave Flowerday]

Originally Posted by Astronouth7303

Ok, I tried that. Get this: ...\user_routines.c:267:Warning [2058] call of function without prototype:

  rnd = Rand();

In C (and C++), function calls are case sensitive. Change "Rand()" to "rand()" and you should be all set.

pwm01=pwm03=Random;
pwm02=pwm04=Random;

Whenever you need to call a function, you need to include the parentheses, even if there aren't any arguments. So your code should look like:

pwm01=pwm03=Random();
pwm02=pwm04=Random();

[Astronouth7303]

Originally Posted by Dave Flowerday

In C (and C++), function calls are case sensitive. Change "Rand()" to "rand()" and you should be all set.


Whenever you need to call a function, you need to include the parentheses, even if there aren't any arguments. So your code should look like:

pwm01=pwm03=Random();
pwm02=pwm04=Random();

THANK YOU!! It compiles fine now.


P.S.- if you dig hard enough, there is an option in the compiler to turn off case-sensitivity but that would be nonconforming oh, well.

[Dave Flowerday]

I'm quite curious as to why you'd want to set your PWM outputs to a random value, though. Most of us prefer to remove random behavior from our robots

[KevinB]

If you are setting the values of the PWMs to a random number everytime the program loop is executed (every ~26ms) .... the motors probably wont do anything ... because theres no way they can change speeds that quickly.

[Astronouth7303]

Originally Posted by Dave Flowerday

I'm quite curious as to why you'd want to set your PWM outputs to a random value, though. Most of us prefer to remove random behavior from our robots

Originally Posted by KevinB

If you are setting the values of the PWMs to a random number everytime the program loop is executed (every ~26ms) .... the motors probably wont do anything ... because theres no way they can change speeds that quickly.

I did this mostly as a programming exercise. But you can use random moving as a defensive technique (grap goal & start random). Specifically, you probably wouldn't use it. But it might surprise your oponents a little.

The full code is:

//...

#include <stdlib.h>


//// DEFINE USER VARIABLES AND INITIALIZE THEM HERE

const int gTime = 75;
#define Left_Forward 0
#define Right_Forward 255
#define Left_Back 255
#define Right_Back 0

//...

//Prototype
int rand(void);

//...

/*******************************************
* FUNCTION NAME: Random
* PURPOSE:       Returns a random char
* CALLED FROM:   this file, Default_Routine
* ARGUMENTS:     none
* RETURNS:       char
*******************************************/
unsigned char Random(void)
{
  unsigned int rnd;
  
  rnd = rand();
  
  rnd = rnd / RAND_MAX;
  return (unsigned char) (rnd & 0xFF);
}

/*******************************************
* FUNCTION NAME: Default_Routine
* PURPOSE:       Performs the default mappings of inputs to outputs for the
*                Robot Controller.
* CALLED FROM:   this file, Process_Data_From_Master_uP routine
* ARGUMENTS:     none
* RETURNS:       void
*******************************************/
//Random Mover

void Default_Routine(void)
{ 
 static unsigned int i_cCount;

 if (i_cCount > 1*gTime)
   {
    pwm01=pwm03=Random();
	pwm02=pwm04=Random();
    i_cCount = i_cCount;
   }
    i_cCount = i_cCount + 1;
  
  printf("i_cCount=%d\n",(int)i_cCount);
} // END Default_Routine();

I shortened it for point of discussion. the //... means I removed something unimportant, or unmodified from the default code.

[KevinB]

    i_cCount = i_cCount;

Is that supposed to be "i_cCount = 0;"? Otherwise ... that line doesn't really do anything ... and your random code will never execute again.

[Astronouth7303]

Originally Posted by KevinB

    i_cCount = i_cCount;

Is that supposed to be "i_cCount = 0;"? Otherwise ... that line doesn't really do anything ... and your random code will never execute again.

My bad. Thank you for pointing it out. You just saved me an hour of debugging.