Problem with Adding Vectors using arrays

[Lonisher]

#include <stdio.h>

int main()
{
	long vect1[2] = {0};
	long vect2[2] = {0};
	long vect3[2];

	printf("Vector Addition\n\n");
	printf("Definitions of vectors using standard form:\n");
	printf("Vector 1-Input the scalars of i, j, and k:\n");
	scanf("%ld %ld %ld", &vect1[0], &vect1[1], &vect1[2]);
	
	printf("Vector 2-Input the scalars of i, j, and k:\n");
	scanf("%ld %ld %ld", &vect2[0], &vect2[1], &vect2[2]);
	
	vect3[0] = vect1[0] + vect2[0];
	vect3[1] = vect1[1] + vect2[1];
	vect3[2] = vect1[2] + vect2[2];


	printf("\nThe resulting vector is:\n");
	printf("%ldi + %ldj + %ldk\n\n", vect3[0], vect3[1], vect3[2]);
	return 0;
}

Ok, so here's my problem. This is intended to be a function within a larger program, but before I can nest it within my menu program I need some help. After I receive the input for vect1, everything is fine, but I can't seem to figure out why after I receive input for vect2 that my vect3[0] value seems to copy the vect3[1] value. any ideas on what I'm doing wrong?

[CommonTater]

You don't want %ld with integers... just use %d ...

Also put a single getchar() call after your first scanf(), it's probably leaving the newline (Enter key) in the buffer.

[Lonisher]

heh, not exactly sure what possessed me to use long instead of int. just making that simple switch was enough to correct the problem. Thanks for the quick reply and help!

[AndrewHunter]

Ok, so here's my problem. This is intended to be a function within a larger program, but before I can nest it within my menu program I need some help. After I receive the input for vect1, everything is fine, but I can't seem to figure out why after I receive input for vect2 that my vect3[0] value seems to copy the vect3[1] value. any ideas on what I'm doing wrong?

You are over running the bounds of your arrays and as such are seeing undefined behavior. In C you get what you ask for, so your declared arrays only have 2 elements, accessed by vect[0] and vect[1]. If you want 3 elements you need to declare all your arrays as long vect[3].

[CommonTater]

heh, not exactly sure what possessed me to use long instead of int. just making that simple switch was enough to correct the problem. Thanks for the quick reply and help!

long, generaly is an abbreviation for long int ... 32 bits on most machines. The %ld formatter is for long long ints which are usualy 64 bits.

As they say... "This ain't that"...

You're welcome.

[CommonTater]

You are over running the bounds of your arrays and as such are seeing undefined behavior. In C you get what you ask for, so your declared arrays only have 2 elements, accessed by vect[0] and vect[1]. If you want 3 elements you need to declare all your arrays as long vect[3].

LOL... He is so! Nice catch...

[Lonisher]

In C you get what you ask for, so your declared arrays only have 2 elements, accessed by vect[0] and vect[1]. If you want 3 elements you need to declare all your arrays as long vect[3].

But I thought arrays defined included the 0 location as an element? Like array[4] would have elements array[0], array[1], array[2], array[3], array[4]

[anduril462]

Nope. array[4] has 4 elements. They go from 0 to 3. Reread the array chapter of your book, carefully.

[Lonisher]

Will do. Seems as though I've got a lot of brushing up to do.

Thanks Folks.

[CommonTater]

But I thought arrays defined included the 0 location as an element? Like array[4] would have elements array[0], array[1], array[2], array[3], array[4]

Ummmm, no... an array of four elements has valid indexes of 0, 1, 2 and 3... go ahead count them...

A common mistake is to confuse "the number of elements" with "the number of the element"...