difference between call by value and call by reference

Call by value :-
Call by Value means that the calling program is passing the value of the literal, or identifier, not a reference to the sending item. The called program can change the parameter in the called program. However, because the subprogram has access only to a temporary copy of the sending item, those changes don't affect the argument in the calling program
Example
static void Classes_CallByValue(Args _args)
{
MyClass_PassingValues passingValues = new MyClass_PassingValues();
Counter counter = 100;
;

info(strFmt("%1", counter));
info(strFmt("%1", passingValues.callByValue(counter)));
info(strFmt("%1", counter));
}
Call-by-reference
Call-by-reference is a way to pass an object as a parameter to a function,that any changes made by the subprogram to the variables it received are visible by the calling program.
Example
static void Classes_CallByReference(Args _args)
{
CustTable custTable;
TmpAccountSum tmpAccountSum;
MyClass_PassingValues passingValues = new MyClass_PassingValues();
Counter counter;
;

while select custTable
{
counter++;

if (counter > 5)
break;

tmpAccountSum.accountNum = custTable.accountNum;
tmpAccountSum.insert();
}

select tmpAccountSum;

info(tmpAccountSum.accountNum);
passingValues.callByReference(tmpAccountSum);
info(tmpAccountSum.accountNum);
}