C scanf int into struct

Question

I am trying to read some integers into a struct. I am having the user enter two 3-dimensional vectors and returning two cross products and the dot product.

It appears to be skipping the second value of the second vector. Here's my code so far:

/** Write a program to calculate cross-products and dot products of 
**  a 3-dimensional vector:
**  
 **    1. Uses a type definition
**    2. Accepts User input of qty(2) 3-dimensional vectors
**    3. Calculate the cross-product of A x B and B x A                         
**    4. Calculate the dot product A * B
**
******************************************************************/


/************* Preprocessor Functions       **********************/
#include <stdio.h>
#include <stdlib.h>


/************ Structured Data Types ***************************/

typedef struct vector
{
    int x;
    int y;
    int z;
} Vector;


/*************   Declare User Functions  **********************/

int dot_product(Vector a, Vector b);
Vector cross_product(Vector a, Vector b);

/************     Begin MAIN LOOP     *************************/

int main(void)
{
/**      Declare variables     **/
    Vector a, b, c;

    printf("Enter the 3 integer components of the first vector: ");
    scanf("%d%d%d", &(a.x), &(a.y), &(a.z));
    printf("Enter the 3 integer components of the second vector: ");
    scanf("%d%d%d", &(b.x), &(b.y), &(b.y));
    c = cross_product(a, b);
    printf("\n\t(%d %d %d) x (%d %d %d) = (%d %d %d)",   a.x,a.y,a.z,b.x,b.y,b.z,c.x,c.y,c.z);
    c = cross_product(b, a);
    printf("\n\t(%d %d %d) x (%d %d %d) = (%d %d %d)", b.x,b.y,b.z,a.x,a.y,a.z,c.x,c.y,c.z);
    printf("\n\t(%d %d %d) * (%d %d %d) = %d\n", a.x,a.y,a.z,b.x, b.y,b.z,dot_product(a, b));

 /***********   AND CUT!  It's a wrap folks!  Take 5!     ***********/    
    return 0;
}

/**********    User Functions to perform the calculations    ****/

int dot_product(Vector a, Vector b)
{
    return((a.x*b.x)+(a.y*b.y)+(a.z*b.z));
}

Vector cross_product(Vector a, Vector b)
{
Vector c;
c.x = (a.y*b.z)-(a.z*b.y);
c.y = (a.z*b.x)-(a.x*b.z);
c.z = (a.x*b.y)-(a.y*b.x);

return(c);

}

If the user enters: 3 2 1 And then enters: 5 6 2

The two vectors used are: [3 2 1] and [5 2 0]

I have tried spaces around the %d in scanf, and no parentheses around &a.x etc.

Thanks for looking and any help is appreciated. Just for full disclosure, this is for a C programming class I am attending.

Solution

You read into b.y twice:

scanf("%d%d%d", &(b.x), &(b.y), &(b.y));

The last one is supposed to be b.z, otherwise b.y is set to 6, then gets overwritten to 2, while b.z is never set (and happens to be 0).

Comments

[Timothy Williams]

Do you have any idea how many times I read through those 4 lines of code trying to figure out what was going on? DOH!!!! Well, hopefully that is the extent of my Homer Simpson moves for the week. HAPPY MONDAY EVERYBODY!!!!

[Spikatrix]

Everyone makes mistakes you know...One tiny mistake is enough to cause a painful headache!! :)

[Zoey Hewll]

A good idea to debug in this situation is to abstract out common parts, eg make a function that reads 3 ints and returns a struct, and test that part in isolation as well as testing the whole