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Doing calculations with arrays - invalid operands to binary

Posted on 2008-06-10
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Last Modified: 2010-04-21
Hi,
I'm new to C programming but feel i'm pretty good at perl so I feel like I really should be able to do this.
I've looked at C tutorials and in several text books but I can't find anything which helps.

All I want to do is do some calculations with arrays of data.
for (i=1; i<=d; i++)
a[i] = b[i] / c[i];
Why does this give me the error message: invalid operands to binary /. I'm using Dev-C++.
The division seems to be causing a problem.
I've tried all data types. I want to use double or float.
I'm adding to an existing C program and earlier in the program there is this code:
for (i=1; i<=x; i++)
y[i] = z[i]  /  t;
This works but mine doesn't.

This type of thing is easy in perl but i've spent ages on this.

Can anyone tell me how to work through arrays and perform calculations on each element or point me to a useful website. Thanks


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Question by:csnell
4 Comments
 
LVL 45

Accepted Solution

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sunnycoder earned 200 total points
ID: 21749650
Hello csnell,

What you have written is fine and should work ... can you post complete code ...

Or you can try this small example.

#include <stdio.h>

int main ()
{
    float a[] = { 1.1, 2.2, 3.3 };
    float b[] = { .1, .2, .3 };
    float c[3];
    int i;

    for (i=0; i<3; i++)
        c[i] = a[i]/b[i];
    for (i=0; i<3; i++)
        printf ("%f\t",c[i]);
}

Regards,
sunnycoder
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LVL 53

Expert Comment

by:Infinity08
ID: 21749651
First, array indexing in C starts at 0, not 1, so most likely :

        for (i=1; i<=d; i++)

has to be :

        for (i=0; i<d; i++)

where d is the length of the array.

About the division not working : can you show how you defined the arrays a, b and c ?
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LVL 40

Expert Comment

by:evilrix
ID: 21749665
It should be more or less the same as Perl... try this...
#include <iostream>
 
int main()
{
	int a[] = {1,2,3,4,5};
	int b[] = {1,2,3,4,5};
 
	for(size_t i = 0 ; i < 5 ; ++i)
	{
		std::cout << a[i] << "/" << b[i] << "=" << a[i]/b[i] << std::endl;
		std::cout << a[i] << "*" << b[i] << "=" << a[i]*b[i] << std::endl;
		std::cout << a[i] << "+" << b[i] << "=" << a[i]+b[i] << std::endl;
		std::cout << a[i] << "-" << b[i] << "=" << a[i]-b[i] << std::endl;
	}
}

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Author Closing Comment

by:csnell
ID: 31465662
Thanks for your help.
It wasn't working because when I had initialized the arrays I had used *. I had looked at what had been done previously in the program for what I thought were arrays. I now know they are pointers!. I have only just begun to understand the basics of pointers so I didn't notice my error.
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