I am just starting to learn how to program in C++, so this question should be an easy one for you experts out there haha. This practice question is bugging me because we haven't learned how to do much in class yet, but I want to have it for tomorrow's class because we get a bonus mark if it's done! I'll give you what I have so far, and the question.

Question

(a) Using only the available operations (shown below), write the C++ code that takes two variables A and B, and puts their product (A times B) into variable C. Your solution must work for the cases...
-where A is zero
-where B is zero
-where A and B are both positive

C++ statements allowed...

Declarations allowed:
int X,Y,Z; //you may declare as many int variables as you need

I/O Operations allowed:
cin >> X;
cout << Y << endl;

Assignment Statements allowed:
X = 0; // 0 is the only constant that may be assigned
X = Y; // copy a variable

Arithmetic Operations allowed:
X++;
X--;

Conditional Statements allowed:
If (<predicate>)
{
}

while (<predicate>)
{
}

Predicates allowed:
X < 0
X > 0
X == 0
X !=0
// You are not allowed to use AND(&&), OR(||), or NOT(!)

This is what I have so far.


I know that isn't much, but as I already said, I have no clue how to do this problem haha. I know that I need usingnamespace std; so that I can use cout and cin. The program that I've written multiplies everything fine, except that it uses a "multiplication operator", how do I do the same thing while sticking to the allowed operators? I know that the program should be more complicated than this.

(b) Suppose you were also not allowed the copy statement X=Y. Could you still make a multiplication routine? Explain.

A million thanks for all the help.

Dan

The trick is to not use the multiply operator. You will have to do it in a loop. It looks like you're allowed to use a while() loop so that should do the trick. Here's how I would do 3 times 5.

1) have an int variable, let's call it result, and initialize it to zero.
2) For 3 times, I would repeat step 3.
3) For 5 times, I would increment result.

Now, result should have your product. I hope this helps. For a hint, use while() loops.

I'm not too sure how to use a while loop though, it looks complicated in my textbook.

I just need to know what the predicate inside the while loop would be...

while (???)

Well, what is it you are trying to do? What is the loop supposed to accomplish -- and how? Figure out how to describe that, but not in code. Write the code from that description. Post your description if you need help...

__________________

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Re: Well, what is it you are trying to do? What is the loop supposed to accomplish -- and how? Figure out how to describe that, but not in code. Write the code from that description. Post your description if you need help...

I'm trying to multiply 'X' by 'Y', without using a multiplication sign. That means I have to add 'X' to itself 'Y' times. For example: to multiply 4*5, I have to add 5 groups of 4 together. Let X = 4, and Y = 5, and Z = answer. So X+X+X+X+X=Z. I'm not sure if this is the correct method though, because I still get caught on what to put in between the brackets in the while loop, and then how to write that equation within the while loop.

This is the new code that I have so far...

If you do that in your loop, it will never end because X never changes. Try doing it like I said before:
See if you can finish the code. Good Luck.