Thread: Unexpected output

So the latest challenge from jumping into c++ is as following.

Code:

Write a function that builds the multiplication table of arbitrary dimensions

This chapter also talks a ton about 2d arrays.

So I've built my program thus far as this.

Code:

#include <iostream>


using namespace std;


int drawTable(int,int);


int main()
{
    drawTable(5,5);
}
/*
0 0 0 0 0
0 1 2 3 4
0 2 4 6 8
0 3 6 9 12
0 4 8 12 16
*/
int drawTable(int x, int y)
{
    int table[x][y];
    int xMax = x;
    int yMax = y;
    int xSlider = 0;
    int ySlider = 0;
    bool loop = true;
    while(loop == true)
    {


        table[xSlider][ySlider] = xSlider * ySlider;
        if(xSlider < xMax && ySlider == yMax)
        {
            loop == false;
        }
        if(ySlider < yMax)
        {
            ySlider++;
        }
        else if(ySlider == yMax)
        {
            xSlider++;
            ySlider = 0;
        }
        cout << table[xSlider][ySlider];
        cin.get();


    }
    return 0;
}

So basically, the idea is that I can use the arrays dimensions as a placeholder, and just multiple them to get that specific spot, so table[0][0] = 0, [0][1] = 0 and so on. However the output actually seems to be randomly generated numbers so I'd like to ask, what am I doing wrong? Am I on the right track? Or have I missed the bus stop completely.

Thanks.

Well, you are printing the values before you calculate them (that is to say, by the time you reach the cout statement, you've changed the values of your index variables, and so you are not printing the value you calculated at the top of the loop). Print before you move your sliders.

Thanks for the reply, I've moved cout to the beginning of the loop, and initialized [0][0] to be set to 0 so I don't get whatever it held before. First 2 numbers always print out ok, after that I'm getting random garbage again.

You're loop = false is broken in two ways -- one, it's a comparison instead of an assignment (your compiler will give you a warning about that line, if you will let it) and two, you are (or would be) setting it to false way too early.

I can't believe I didn't notice I used == whoops. I guess tired programming will do that. Also, I don't understand what you mean by saying I set it to false too early, If its conditions are met the loop should be done solving the table. At least that's how I see it.

Originally Posted by CrimsonMagi

I can't believe I didn't notice I used == whoops. I guess tired programming will do that. Also, I don't understand what you mean by saying I set it to false too early, If its conditions are met the loop should be done solving the table. At least that's how I see it.

If your table is only one row long, then yes. If you want more than one row, then you could be in trouble.

Thank you for the continued replies tabstop. at the time of writing this, I had been about 2 days without sleep so I wasn't thinking very well. So first, let me say thank you for the patience. Second I've got it fully functional and i'll leave it here in case anyone else ever needs the solution. Feel free to give me feedback how I could make this program better.

Code:

//Multiplication table, jumping into c++ 2d array
#include <iostream>


using namespace std;


int drawTable(int,int);


int main()
{
    drawTable(5,5);
    return 0;
}
/* table added in for visual representation of the problem.
0 0 0 0 0
0 1 2 3 4
0 2 4 6 8
0 3 6 9 12
0 4 8 12 16
*/
int drawTable(int x, int y)
{
    int table[x][y];
    int xMax = x;
    int yMax = y;
    int xSlider = 0;
    int ySlider = 0;
    table[0][0] = 0;
    bool loop = true;
    while(loop == true)
    {




        cout << table[xSlider][ySlider] << " ";
        ySlider++;
        if (ySlider == yMax)
        {
            ySlider = 0;
            xSlider++;
            cout << endl;
        }
        if (xSlider == xMax)
        {
            loop = false;
        }
        table[xSlider][ySlider] = xSlider * ySlider;


    }
    return 0;
}

You can literally do it with just two for loops that are nested and normal arithmetic.