# Solved: C# Array Multiplying

Discussion in 'Software Development' started by supergoten, Apr 2, 2010.

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1. ### supergotenThread Starter

Joined:
Apr 14, 2009
Messages:
28
This is probably a really simple problem.

I have three arrays here. The third array needs to be the product of the first two... how do I multiply the arrays for each value? I know there has to be a for loop but i'm not sure how it should be written.

Code:
```   double[] array1 = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
double[] array2 = { 2, 4, 6, 8, 10, 12, 14, 16, 18, 20 };
double[] array3;```

2. ### DYS

Joined:
Dec 28, 2008
Messages:
462
So do you want to multiple, for example, element 1 in array 1, with element 1 in array 2, and so on?

I'm not a genius like others here are, but if you're doing straight multiplication, why do the arrays need to be doubles? They can be integers, can't they?

3. ### supergotenThread Starter

Joined:
Apr 14, 2009
Messages:
28
Yes, that's the way it could be done.
And yeah they could be done as integers i suppose.

Thanks for any help you can give.

4. ### DYS

Joined:
Dec 28, 2008
Messages:
462
Code:
```for (int i = 0; i<=9; i++)
{
array1[i] * array2[i];
}
```
I think the code should be something like that, although I'm working from Java, rather than C#, as I've only used C# to do XNA, and I can't really recall having to write a loop to multiply stuff.

Anyway, I'm not too sure how to add each answer to each element in the third array. I think someone who knows more about this will have to answer that for you. But I hope (for myself as well) that I have been some help.

5. ### supergotenThread Starter

Joined:
Apr 14, 2009
Messages:
28
I think it's close, but it still has an error.... you've been a big help though... does anyone else have any help?

6. ### MMJGuest

Joined:
Oct 15, 2006
Messages:
3,625
Exactly what items do you want to multiply together?

7. ### DYS

Joined:
Dec 28, 2008
Messages:
462
Okay mate. Glad I could be of some help at least. Like I said, I had Java in mind, as I have more experience of that.

MMJ, supergoten wants to multiply each element against the corresponding position in the respective arrays.

So basically:
1 * 2
2 * 4
3 * 6

and so on... Or at least that's how I've understood it.

8. ### MMJGuest

Joined:
Oct 15, 2006
Messages:
3,625
PHP:
``` for (int i = 0; i <= 9; i++){    array3.Add(array1[i] * array2[i]);} ```

9. ### DYS

Joined:
Dec 28, 2008
Messages:
462
Would he need to tell the third array to increase the element position each time? Like:
Code:
```for (int i = 0; i <= 9; i++)
{
array3[i].Add(array1[i] * array2[i]);
}
```
Kinda learning myself here too I guess ha ha.

10. ### supergotenThread Starter

Joined:
Apr 14, 2009
Messages:
28
Ok, this is what i have right now.

Code:
```using System;
using System.Collections.Generic;
using System.Text;

namespace ArrayProgram
{
class Program
{
static void Main(string[] args)
{
double[] array1 = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
double[] array2 = { 2, 4, 6, 8, 10, 12, 14, 16, 18, 20 };
double[] array3;

for (int i = 0; i <= 9; i++)
{
array3.Add(array1[i] * array2[i]);
}

}
}
}
```
There's still an error though, 'System.Array' does not contain a definition for 'Add'

11. ### MMJGuest

Joined:
Oct 15, 2006
Messages:
3,625
Sorry, Add is a function for lists, which have more use in C# then arrays

Try this:

Code:
```using System;
using System.Collections.Generic;
using System.Text;

namespace ArrayProgram
{
class Program
{
static void Main(string[] args)
{
double[] array1 = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
double[] array2 = { 2, 4, 6, 8, 10, 12, 14, 16, 18, 20 };
double[] array3;

for (int i = 0; i <= 9; i++)
{
array3[i] = array1[i] * array2[i];
}

}
}
}```

12. ### supergotenThread Starter

Joined:
Apr 14, 2009
Messages:
28
It still isn't working

I'm not sure if this code is any better, it still isn't right though.

Code:
```   double[][] anArray = new double[2][];
anArray [0] = new double [] { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
anArray [1] = new double [] { 2, 4, 6, 8, 10, 12, 14, 16, 18, 20 };
double[] array3 = new double[10];

for (int i = 0; i <= 9; i++)
{
array3[i] = anArray[0] * anArray[1];
}
}
}
}```

13. ### MMJGuest

Joined:
Oct 15, 2006
Messages:
3,625
Code:
```using System;
using System.Collections.Generic;
using System.Text;

namespace ArrayProgram
{
class Program
{
static void Main(string[] args)
{
double[] array1 = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
double[] array2 = { 2, 4, 6, 8, 10, 12, 14, 16, 18, 20 };
double[] array3 = new double[10];

for (int i = 0; i <= 9; i++)
{
array3[i] = array1[i] * array2[i];
}

}
}
}```
Post any error code.

14. ### supergotenThread Starter

Joined:
Apr 14, 2009
Messages:
28
I copied that and it seems to be working! Thank you so much

15. ### MMJGuest

Joined:
Oct 15, 2006
Messages:
3,625
NP, I don't have VS so I couldn't give the the right answer on my first reply.

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