Ej3C

#include<stdio.h>
#include<stdlib.h>

#define offsetof(structure, field) (size_t)(&((structure*)0)->field)

struct person_struct
{
    float height;
    int age;
    float weight;
};

typedef struct person_struct person;

int sumar(const void* arreglo, size_t tamanio_elemento, size_t offset_campo, size_t cant_elementos);

int main (void)
{
    int i;
    int result;
    person ppl_list[10];

    for (i=0; i<10; i++)
    {
        ppl_list[i].height = 1.4 + i/10.;
        ppl_list[i].age = 15 + i;
        ppl_list[i].weight = 50. + 2.* i;
    }

    result = sumar(&ppl_list[0],sizeof(person), offsetof(person, age), sizeof(ppl_list)/ sizeof(ppl_list[0]));
    printf("El resultado es: %i\n", result);

    return EXIT_SUCCESS;
}

int sumar(const void* arreglo, size_t tamanio_elemento, size_t offset_campo, size_t cant_elementos)
{
    int result, i, current_value;
    char * pointer_to_element;

    result = 0;

    pointer_to_element = (char*) arreglo;
    pointer_to_element += offset_campo;

    for (i=0; i<cant_elementos; ++i)
    {
        current_value = *(int*) pointer_to_element;
        result += current_value;
        pointer_to_element += tamanio_elemento;
    }
    return result;
}