What is the difference between a function and a subroutine?

Question

What is the difference between a function and a subroutine? I was told that the difference between a function and a subroutine is as follows:

A function takes parameters

Answer 1

Both function and subroutine return a value but while the function can not change the value of the arguments coming IN on its way OUT, a subroutine can. Also, you need to define a variable name for outgoing value, where as for function you only need to define the ingoing variables. For e.g., a function:

double multi(double x, double y) 
{
  double result; 
  result = x*y; 
  return(result)
}

will have only input arguments and won't need the output variable for the returning value. On the other hand same operation done through a subroutine will look like this:

double mult(double x, double y, double result) 
{
  result = x*y; 
  x=20; 
  y = 2; 
  return()
}

This will do the same as the function did, that is return the product of x and y but in this case you (1) you need to define result as a variable and (2) you can change the values of x and y on its way back.