Thread: running through a loop using pointers

I am working on a homework assignment an have spent quite some time trying to figure out why my code is not running right when I convert my loop to using pointers. I have gone through and debugged my code and found that it is sending a segmentation fault when it hits the if statement the sends it back through the loop. If anyone can help me it would be greatly appreciated.

Code:

 
#define ARRAY_SIZE   10000

double  *array = calloc(ARRAY_SIZE, sizeof(double));
double  sum = 0;

int *max, *end;
max = &end[ARRAY_SIZE];
								
loop:   //loops through array and adds up all elements of array
    sum = sum + array[0] + array[1] + array[2]; 

if(*array < *max) // this is where the debugger throws the segmentation fault error
	goto loop;

This is not my whole code, but I know the other parts of the code work, so I am just posting the relevant parts.

Thanks
boy

Is there some reason you are using a goto instead of for or while or do while? Also, you are derefererencing the pointers to control your loop. You shouldn't be.


Quzah.

You may benefit from reading through:
Lesson 3-Loops
Lesson 6-Pointers
Lesson 8-Arrays

Originally Posted by boy

Code:

loop:   //loops through array and adds up all elements of array
    sum = sum + array[0] + array[1] + array[2];

when do you add the other elements of your array?

Originally Posted by boy

Code:

int *max, *end;
max = &end[ARRAY_SIZE];

It throws the segfault because you never initialize end to anything, yet then you assign some random value to max. You should read through your book again.

Originally Posted by boy

The point of the assignment was to optimize the loop, after trying the for and while loop methods, I found it faster to use the goto; for some reason. I am new to pointers so I was trying to follow an example to work with my code. If I don't add the de-referencing symbol, the compiler gives me the warning:" assignment makes pointer from integer without a cast".

I'd worry about actually getting it working before I started optimizing anything.

Code:

int *max, *end;
max = &end[ARRAY_SIZE];

What is it you think end is pointing at here?

Code:

array = allocate space
for( current = array, end = array + ARRAY_SIZE; current < end; current++ )
    ...do stuff

Quzah.

No. Your compiler should be complaining at you.

1. You only allocate 1 int. (That may be what you intended, but I doubt it.)
2. You immediately toss away what you have assigned by assigning it something else (an integer, instead of an address).


Quzah.

Originally Posted by boy

This:

Code:

int *max = malloc(sizeof(int));
max = ARRAY_SIZE;

should be:

Code:

int *max = malloc(ARRAY_SIZE * sizeof(int));

EDIT: That is assuming, you want max to be your array.