Why do we leave some structure variables out of the curly brackets?

Question

I'm trying to understand struct in C. I couldn't get the idea about this definition below. Why do we leave aCard, deck[ ] and *cardPtr out? What is the difference between including them in and leaving them out?

 struct card {
    char *face;
    char *suit;
 } aCard, deck[52], *cardPtr;

Answer 1

You are mixing things up. A struct card has the members face and suit. But there are three variables using the struct card type, namely aCard, deck, cardPtr.

Alternatively one could have written:

typedef struct {
    char *face;
    char *suit;
} Card;

Card aCard, deck[52], *cardPtr;
// or even
Card aCard;
Card deck[52];
Card *cardPtr;

For the typedef have a look at: Why should we typedef a struct so often in C? (It goes into the typedef struct { ... } Foo; vs struct Foo {...} debate).

Answer 2

Your piece of code could be written like this which makes it clearer:

struct card {          // define the struct card
    char *face;
    char *suit;
 };

struct card aCard;     // declare a variable "aCard" of type "struct card "
struct card deck[52]   // declare an array of 52 variables of type "struct card"
struct card *cardPtr;  // declare a variable "cardPtr" of type "pointer to struct card"