Question

I am having trouble with structure definitions. I understand the syntax but can’t use it correctly to make a working program. My assignment is to define a structure type element_t to represent one of the elements of the periodic table. Components should include atomic number, name, symbol, class, weight and a seven element array of integers for the number of electrons in each shell. The following are the components of an element_t structure for sodium.

11 Sodium Na alkali_metal 22.9898 2 8 1 0 0 0 0

Define and test I/O functions scan_element and print_element.
Here is my code… but no worky. I dont understand why the compiler says I haven’t initialized element_t. Thanks in advance.

***Ended up with the following code, also added the appropriate loops and & signs although it is not shown below and everything worked fine. I was curious to know how the powerpoint slides in my class used {2 8 1 0 0 0 0} to populate the int array instead of a loop. The book I am using uses the loop method as well but I wanted to try the {} way of doing it. Thanks again.

#include <stdio.h>
#include <string.h>

typedef struct  {
    int atomic_num;
    char* element_name; revised:    char element_name[25];
char* element_symbol; revised:   element_symbol[2];
    char* element_class; revised:   char element_class[25];
    double atomic_weight;
    int electrons[7];
} element_t;

int scan_element(); revised: element_t scan_element();
void print_element(element_t my_element);

int scan_element() {
    element_t my_element;

    printf("Enter Atomic Number> ");
    scanf("%d", my_element.atomic_num);

    printf("Enter Element Name> ");
    scanf("%s", my_element.element_name);

    printf("Enter Element Symbol> ");
    scanf("%s", my_element.element_symbol);

    printf("Enter Element Class> ");
    scanf("%s", my_element.element_class);

    printf("Enter Atomic Weight> ");
    scanf("%lf", my_element.atomic_weight);

    printf("Enter Electons in each shell> ");
    scanf("%d", my_element.electrons);

    print_element(my_element);
    return 0;
}

void print_element(element_t my_element) {
    printf("%d %s %s %s %lf %d \n",my_element.atomic_num,my_element.element_name, my_element.element_symbol,my_element.element_class,my_element.atomic_weight,&my_element.electrons);
}

int main()
{
    scan_element(); revised: print_element(scan_element());

    return 0;
}

Answer 1

I’ve identified some problems in your code:

1)When reading with scanf non-pointer types(like int or float), use the & operator. Scanf needs a pointer to your variable, not the variable itself.

2)If you declare your strings as dynamic (char*), be sure to use malloc to allocate memory for them. Otherwise declare them statically like char my_string[30].

3)Your scan_element function should return an element_t structure, not an int. Alternatively you could pass a pointer to an existing element_t structure and modify it in your function.

4)You cannot read/print a int array directly using scanf/printf. Every element must be read separately.

5)Your scan_element function shouldn’t probably contain print_element 😛

If you want to learn more about Console I/O in ANSI C, perhaps this article could be useful.

Here is the corrected code:

include <stdio.h>
#include <string.h>

typedef struct  {
    int atomic_num;
    char element_name[30];
    char element_symbol[3];
    char element_class[30];
    double atomic_weight;
    int electrons[7];
} element_t;

element_t scan_element();
void print_element(element_t my_element);

element_t scan_element() {
    int i = 0;
    element_t my_element;

    printf("Enter Atomic Number> ");
    scanf("%d", &my_element.atomic_num);

    printf("Enter Element Name> ");
    scanf("%s", my_element.element_name);

    printf("Enter Element Symbol> ");
    scanf("%s", my_element.element_symbol);

    printf("Enter Element Class> ");
    scanf("%s", my_element.element_class);

    printf("Enter Atomic Weight> ");
    scanf("%lf", &my_element.atomic_weight);

    for(i = 0; i<7; i++)
    {
        printf("Enter Electon - electron nr %d\n",i);
        scanf("%d", &my_element.electrons[i]);
    }

    return my_element;
}

void print_element(element_t my_element) {
    int i;
    printf("%d %s %s %s %lf\n",
           my_element.atomic_num,
           my_element.element_name, 
           my_element.element_symbol,
           my_element.element_class,
           my_element.atomic_weight);
    for(i = 0; i<7; i++)
    {
        printf("%d",my_element.electrons[i]);
    }
    puts("\n");
}

int main()
{
    element_t val = scan_element();
    print_element(val);

    return 0;
}