I need help in the Syntax of this

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4

But an array is just an alternative notation for pointer arithmetic, and arrays are normally passed by reference anyway...

So the following would work the same as Nick's example, with more obvious syntax:

void func( float args[3] )
{
  args[0] += 1;
  args[1] *= 2;
  args[2] /= 3;
}

void setup()
{
  float foo[3] = { 5, 6, 7 };
  func( foo );
}

void loop()
{
}

This also reinforces the point that you should be careful not to alter the values in an array passed to a function in place, unless you want those changes to affect the array in the calling function as well.