Output for pass-by-value and pass-by-name

Question

I am needing to find the result of the following code when x and y are passed-by-value and also when passed-by-name.

PROGRAM EX1; 
int i; //global
int A[3]; //global

    PROCEDURE P1(int x, int y)
    Begin
        y:=2; 
        PRINT(x); 
        i:=3; 
        PRINT(x); 
        i:=3; 
        PRINT(x); 
        PRINT(y); 
    End; 
BEGIN //main
    A[1]:=7; A[2]:=13; A[3]:=11; 
    i:=1; 
    P1(A[i],i); //first call
    P1(i,A[i]); //second call
END.

Here is what I concluded if x and y are pass by value: Outputs: 13, 11, 11, 3 Second Output: 1, 3, 3, 11. If that is wrong please help me understand why.

I am also not sure how pass-by-name would work in this code from the examples I have seen. Please help with that as well.

Assume static scoping.

Did you try to google about that is the meaning of parameter passing methods? Also, you can't pass parameters to a function/procedure sometimes in one way and sometimes in another. The function/procedure declaration established what method is going to be used. Last, if you pass by value, any change to their values within the procedure/function is lost once the procedure/function completes. — FDavidov, Nov 13 '16 at 15:24
This is just theoretic, what would the code output if it was in run using different parameter passing. And yes I have googled and have a textbook on the different passing methods but I am needing a little more instruction to help me understand. — KNuz, Nov 13 '16 at 15:34

score 0 · Answer 1 · answered Nov 14 '16 at 06:01

I will ignore during the description the fact that your code would most likely fail to compile/run, and will only address your specific question.

Regardless of the mechanism used to pass the parameters (by value or by name), the assignments to the variable i are meaningless: when passed by value, there is no meaning at all (within the function P1) the fact that the source parameters may be arrays; when passed by name and you pass A[i] where i=1, what reaches the body of function P1 is A[1] and hence changes to i would have no effect at all.

So, in both cases (by value and by name) you will get the same result, meaning: 7,7,7,2 for the first invocation, and 1,1,1,2 for the second.

Output for pass-by-value and pass-by-name

1 Answers1