C函数返回值的范围

Question

int Mul (int x)
{
   int y =0;
   y = x *3;
   return y;
}

int Main(void)
{   
   int var =0;
   scanf ("%d", &var);
   int result =0;
   result = Mul(var);
   printf ("%d", result);
}

Now my question is:
The variable y is created on the stack and when the function Mul returns, it gets cleared. Then how it is assigned to result?

result = Mul(var);

Answer 1

C considers the function "Mul" to have this value upon return, as though it were a variable. Note that Mul is declared as an int. Using "return" puts the value of y on the stack to be used in the assignment to "result". This value is popped from the stack which in effect clears it.

Answer 2

The statement return y; Does not return the value of y but a copy of the value of y. This copy is stored in the result variable. When you execute the code again with new values for x and y, the old values are overwritten.

Answer 3

1. You are returning the value of the variable (y) not the variable it self. Also variable "y" is local to mul function , so you cant return "y" as its scope is local to that function.

2. Whenever there is function call other than the void data type, the function call statement is replaced by the value that function is returning.

For eg.

In your case if x=3 then y= 3*3 evaluates to 9 thus

y=9

and

return y 

simply means return 9 just like you return 0.

so the expression

result=mul(var) //is replaced by result=9.

I think this is enough of explanation