Unusual Output from C Array Code

Question

As a simple attempt at a coding exercise in a book I've been reading, I wrote the following code:

#include <stdio.h>

int main() {
        double data[12][5];
        int i;
        double t = 2.0;

        for(i = 0; i < 12; i++) {
                data[i][0] = t;
                t += 0.1;
        }

        for(i = 0; i < 12; i++) {
                data[i][1] = 1.0 / data[i][0];
                data[i][2] = data[i][0] * data[i][0];
                data[i][3] = data[i][2] * data[i][0];
                data[i][4] = data[i][3] * data[i][0];
        }

        printf("x 1/x x^2 x^3 x^4\n");

        int row;
        int column;

        for(row = 0; row < 12; row++) {
            printf("%10lf %10lf %10lf %10lf %10lf\n", data[i][0], data[i][1], data[i][2], data[i][3], data[i][4]);
        }

        return 0;
}

However, when I run it the output appears as at ideone.com: http://ideone.com/KLWtdk. According to how I think the code should run, the far left column should be a range of values inclusive from 2.0 to 3.0 with a 0.1 step size. This is not the case, however.

Also, while chatting on IRC, I was told to not use tabs when printing tables of data but instead to use printf widths. I want to be able to have a header over each column in text, however - is there any way to do that?

The way to get the labels aligned is printf("%10s %10s %10s %10s %10s\n", "x", "1/x", "x^2", "x^3", "x^4"); Use the same width in the string formats as in the numeric formats. This right justifies the labels; to left justify, use %-10s instead. — Jonathan Leffler
– Jonathan Leffler, Commented Jun 20, 2014 at 6:49
@JonathanLeffler Do you mind if I incorporate your suggestion into my answer (with attribution of course) for the sake of completeness? — shree.pat18
– shree.pat18, Commented Jun 20, 2014 at 7:06

shree.pat18 · Accepted Answer · 2014-06-20 07:12:17Z

4

Your problem is that you declare iteration variable row, but use i for index in the print statement. Since the value of i is independent of the value of row, every iteration will give you the same values, and they won't be the right ones.

You can resolve this by accessing the array elements as data[row][column_index] e.g. data[row][0]

Regarding the formatting, as mentioned by @JonathanLeffler:

The way to get the labels aligned is

printf("%10s %10s %10s %10s %10s\n", "x", "1/x", "x^2", "x^3", "x^4");

Use the same width in the string formats as in the numeric formats. This right justifies the labels; to left justify, use %-10s instead.

edited Jun 20, 2014 at 7:12

answered Jun 20, 2014 at 6:44

shree.pat18

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1 Comment

phuclv Over a year ago

@useanalias actually it's afternoon in Singapore

ayusha · Accepted Answer · 2014-06-20 09:20:27Z

0

In the last loop you use different variable for iteration and different for printing values. variable i used for declaration,condition check & increments/decrements.

i is that variable.

Another variable row used for printing values which have garbage value and not changed throughout the loop.

row is that variable

answered Jun 20, 2014 at 9:20

ayusha

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Comments

Sanket Parmar · Accepted Answer · 2014-06-20 06:47:43Z

-1

Use data[row][0], data[row][1], data[row][2], data[row][3] while printing results.

answered Jun 20, 2014 at 6:47

Sanket Parmar

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1 Comment

shree.pat18 Over a year ago

I didn't downvote, but may be because you haven't provided an explanation of why your answer will solve the issue.

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