Random Numbers

Technical Programming
#1

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 :confused:

Help?!?

#2

You might want to try


rnd = rand();

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

#3

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. :o

#4

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();
#5

:cool: 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 :smiley: but that would be nonconforming :rolleyes: oh, well.

#6

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 :wink:

#7

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.

#8

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
",(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.

#9 

    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.

#10

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