Question

Can I do something like this? Will this work?

double *vec_subtraction (char *a, char *b, int n)
{   
    double *result;
    int i;

    for(i=0; i<n; i++)
        result[i] = a[i]-b[i];

    return result;
}

and then in main:

double *vec=vec_substraction(a, b, n);
for(i=1; i<n; i++)         
    printf("%d", vec[i]);

a and b are vectors with the same number of elements, n is number of elements.

Answer 1

Yes you can, but you need to allocate memory for result somewhere.

Basically, you can either allocate the memory inside vec_subtraction or outside vec_subtraction, if you allocate outside you can do this statically or dynamically.

If you’re going to allocate inside:

double *vec_subtraction (char *a, char *b, int n) {
    double *result = malloc(sizeof(double)*n);
    int i;
    for(i=0; i<n; i++)
        result[i] = a[i]-b[i];

    return result;
}

and in main:

double *vec;
// ...
vec = vec_subtraction(a, b, n);
// ...
free(vec); 

Don’t forget to free the result of the call to vec_subtraction sometime later.

---

If you’re going to allocate outside you need to pass in a pointer to the memory:

void vec_subtraction (char *a, char *b, int n, double *result) {
    int i;
    for(i=0; i<n; i++)
        result[i] = a[i]-b[i];
}

in main:

// choose one of:
// double *vec = malloc(sizeof(double)*n);
// double vec[10]; // where 10= n.
vec_subtraction(a, b, n, vec);

// if you used *vec = malloc... remember to call free(vec).