Segmentation Fault Error; Absolute Value Table

Question

I've been hammering myself on to this homework for a while now. And I can't seem to find what's wrong with it.

My question is why do I keep getting segmentation fault errors everytime I execute this program.

/* Description: A program that takes an input array argument with type double values and displays a table of those inputs and their absolute values.
*/

...

int main() /* Main Function */
{
    /* Variables */

    int size=5,n;
    double value[n];
    double table;

    /* Instructions and Input */

    for(n=0;n<size;n++){
            printf("\nPlease enter value #%d:\n",n);
            if(n=size-1){printf("\nPlease enter the last value.\n");}
            scanf("%lf",&value[n]);
    }

    /* Recalling the Function and Output */

    printf("\nValue\t|Value|\n"); /* Table Header */
    table=abs_table(value[n],size); /*Absolute Value Table */

    return 0;
}

double abs_table(double value, int size) /* Absolute Value Function */
{
    int i,j; /* Counter Variables */
    double v;

    for(j=1;j<=size;j++){ /* For the Number of rows */
            for(i=0;i<=size;i++){ /* For the number of columns */
                            v = abs(value); // For the absolute values */
                            printf("\n%g\t%g\n",value,v);
                    }
    printf("\n"); /* To make sure the rows display on their own line */
    }

    return;
}

`double value[n];` `n` isn't initialised, thus undefined. It shouldn't even be allowed to compile, in any case, enable compiler warnings (`-Wall` for GCC). — Kninnug, Oct 28 '13 at 21:11
Addressing the only question asked, because you're invoking undefined behavior due to an indeterminate value in a local variable. — WhozCraig, Oct 28 '13 at 21:23

Igor Popov · Answer 1 · 2013-10-28T21:39:23.577

1

Many errors are in your program:

Array cannot be initialized with variable length n: double value[n];.
One additional = is missing in if(n=size-1).
Even if you initialized array correctly with length n (point 1) then scanf("%lf",&value[n]); will write to a memory location beyond the length of the value array.
abs is coded for integer but not double: v = abs(value);.
...possibly some more errors but the list is already quite long.

edited Oct 28 '13 at 21:39

answered Oct 28 '13 at 21:19

Igor Popov

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I don't think he wants to print the address of `n`, so an ampersand isn't necessary. – Kninnug Oct 28 '13 at 21:21
Indeed, my mistake. Removed. – Igor Popov Oct 28 '13 at 21:39

Tu Bui · Accepted Answer · 2013-10-28T21:37:19.397

1

there are several errors in your code:

Error1: in main() you declare double value[n]; I believe what you want is double value[size];

Error2: in main() statement if(n=size-1) should be changed to if(n==size-1)

Error3: in main() you call function table=abs_table(value[n],size); it should be table=abs_table(value,size);

Error4: you define function double abs_table(double value, int size){...} it should be double abs_table(double value[], int size){...}

Error5: inside function abs_table I actually don't know what you are trying to display here. One spot is that variable i should run from 0 to size-1, another spot is that you should return something

edited Oct 28 '13 at 21:37

answered Oct 28 '13 at 21:29

Tu Bui

1,660
5
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He's not using `value` as an array inside `abs_table`, so it's technically not wrong to accept & pass a (normal) `double`. – Kninnug Oct 28 '13 at 21:31
You could be right, Kninnug. It is all up to him. According to the `for` loop inside the `abs_table` function I guess he actually wants to pass an array to it – Tu Bui Oct 28 '13 at 21:40

score 0 · Answer 3 · answered Oct 28 '13 at 21:20

In main you declare int n without initialising it and subsequently double value[n]. Therefore n has an undefined value and thus value is of undefined size. I think you meant to declare double value[size], which you did initialize.

Also, abs_table is supposed to return a double but you're returning void.

Segmentation Fault Error; Absolute Value Table

3 Answers3