Thread: how to pass array by reference

Hey guys, I have an array of 3 elements and a function that can take an array of 4 elements, I want to manipulate the 4 elements in the function and pass them mack by reference, hopefully my sample code will enlighten my problem.

Code:

void doubleElements(int *array[3]);

int main(void)
{
    int array1[3];
    array1[0] = 2;
    array1[1] = 4;
    array1[2] = 6;
    array1[3] = 8;

    doubleElements(&array1);
 
}

void doubleElements(int *array[3])
{
     array[0] = array[0]*2;
     array[1] = array[1]*2;
     array[2] = array[2]*2;
     array[3] = array[3]*2;
}

Is there something wrong here??? Obviously I want:
array1[0] = 4
array1[1] = 8
array1[2] = 12
array1[3] = 16

Appreciate the help!

Your array in main is under-sized - 0 to 3 IS 4 elements.

In the call to the function, just use the name of the array, no & before it.

Why not use a loop inside your function?

Woops my original sentace should have been:
"I have an array of 4 elements and a function that can take an array of 4 elements....."

no & before it you say... Il give it a whirl thanks!

Probably you meant doubleElements(array1, sizeof(array1)/ sizeof(array1[0]) );

What is the difference between doubleElements( array1, sizeof(array1) / sizeof(array1[0]) ); and doubleElements(array1, sizeof(array1)/ sizeof(array1[0]) ); ????

What is the difference between doubleElements( array1, sizeof(array1) / sizeof(array1[0]) ); and doubleElements(array1, sizeof(array1)/ sizeof(array1[0]) ); ????

One is on line 1, and the other is on line 2!

Nothing. Elysia fixed it.

Had you going there, eh?

k... well I've tried that code but it does not work, obviously my sample code is much different to what I am trying to write but surely the error is the same??? if I use:
doubleElements( array1, sizeof(array1) );
instead of what Elysia said:
doubleElements( array1, sizeof(array1) / sizeof(array1[0]) );
then it works but am i doing something i shouldnt? like I said the code I am writing is performing a different task (HC12 microcontroller converting 4 analogue inputs to digital ones and turning on a LED if the digital value of one channel is larger than a certain interger that I define)

OK here is pretty much my code:

Code:

#include <hidef.h>      //common defines and macros 
#include "derivative.h" //derivative-specific definitions 
#include "ADC.h"        //allows convenient use of ADC
#include <assert.h>



void DisSensors(int SampleSize, int OnThresh, int OffThresh, int* result, size_t size); 


void main(void)
{
  int DS[3]; //Distance Sensors
  int PS1=0, PS2=0, PS3=0, PS4=0;  //Photo sensors
  int i; 
  int average=0;
  EnableInterrupts;
  ADCInit();      //initialises the ADC before first use
  /* delay(5000); // 5 second delay before start of the round NEEDS ACCURATE CALIBRATION  */ 

  DDRT = (0xFF);
  PTT = (0x00);
      
  
  for(;;)
  {
       DisSensors(10, 100, 70, DS,sizeof(DS)/ sizeof(DS[0]) ); 
        
  } /* loop forever */
  /* please make sure that you never leave main */
}


void DisSensors(int SampleSize, int OnThresh, int OffThresh, int* result, size_t size)
{
    int i;
    assert(size >= 4);
    result[0] = 0;
    result[1] = 0;
    result[2] = 0;
    result[3] = 0;
    for(i=1;i<=SampleSize;i++) 
    {
      ADCDoConversions(); // trigger convertion
      result[0] = result[0] + ATDDR2;
      result[1] = result[1] + ATDDR3;
      result[2] = result[2] + ATDDR4;
      result[3] = result[3] + ATDDR5;
    }
    result[0] = result[0]/SampleSize;
    result[1] = result[1]/SampleSize;
    result[2] = result[2]/SampleSize;
    result[3] = result[3]/SampleSize; 
    for(i=0;i<=0;i++)
    {
      if(result[i] >= OnThresh)
      PTT = 0x01;//result[i] = TRUE;
      else if(result[i]<=OffThresh)
      PTT = 0x00;//result[i] = FALSE;
    } 
}

Doing it this way it compiles but when I go into the debugger and try run the program it doesnt run??? sorry for the length of code...