Why I need to use ref keyword in both declaration and Call?

Question

Duplicate of: What is the purpose of the “out” keyword at the caller?

Why I need to use 'ref' keyword in both declaration and Call.

void foo(ref int i)
{

}

For example, Consider above function. If I will call it without ref keyword as

foo(k);

it will give me error :

Argument '1' must be passed with the 'ref' keyword

Why isn't it enough to just specify in the method signature only ?

Answer 1

This is because ref indicates that the parameter should be passed in by reference. It is something like pointer in C++

For example;

void CalFoo()
{
  var i=10;
  foo(ref i);  //i=11
}
void foo(ref int i)
{
   i++;
}

but

void CalFoo()
{
  var i=10;
  foo(i);  //i=10
}
void foo(int i)
{
   i++;
}

I think you can have both foo(ref int) and foo(int) in one single class. So if you don't specify the ref.. how does the compiler knows which one to call?