Comparing Stacks of Doubles resulting in Always Equal

Question

I'm trying to compare two stacks, to see if they are equal. Unfortunately, this code makes it so all of my comparisons say the stacks are equal, even if the stacks are not.

Stack_implementation.cpp snippet:

int DoubleStack::operator==(DoubleStack& rhs)
{
    int equal = 1;
    for (int i = 0; i <= tos; i++)         //tos is the top of the stack indicator
    {                                      //it tells how big the stack is
        if (data[i] != rhs.data[i])
        {
            equal = 0;
            break;
        }
    }
    return equal;
}

main.cpp relevant snippet:

{
    cout << "Comparing stacks..." << endl;
    if (stack1 == stack2)
        cout << "stack1 = stack2." << endl;
    else
        cout << "stack1 != stack2." << endl;
}

The output is always stack1 = stack2

Anyone know what's wrong?

This code is wayyyy too noisy. Why all the typing? `{ for (int i = 0; i<= tos; ++i) if (data[i] != rhs.data[i]) return 0; return 1; }` — Kerrek SB, Aug 11 '14 at 20:52
@Kerrek SB, The user will enter how large the stack can be at the beginning of the program. — ardunn, Aug 11 '14 at 20:56
You haven't shown any evidence that the stacks are not equal. — juanchopanza, Aug 11 '14 at 20:58

score 1 · Accepted Answer · answered Aug 11 '14 at 20:56

The first check should be for the size of stacks; if sizes are not the same, stacks cannot be equal. The code as written can go beyond end of one of the stacks.

You can also return as soon as you find one different item. There's no need to continue with the loop.

bool DoubleStack::operator==(DoubleStack& rhs)
{
    if (tos != rhs.tos) {
        return false;
    }

    for (int i = 0; i <= tos; i++)         //tos is the top of the stack indicator
    {                                      //it tells how big the stack is
        if (data[i] != rhs.data[i])
        {
           return false;
        }
    }
    return true;
}

Thank you. I didn't think about the size of them, I guess it was just checking the elements. — ardunn, Aug 11 '14 at 21:04

Comparing Stacks of Doubles resulting in Always Equal

1 Answers1