Thread: Prototypes & Structures

1. '*' means a pointer. ie, str is a pointer to a character -- that is holds an address of a character. In this case, the start of a character in a string.

size is how many elements in the array I assume (since you posted no code), by 'the array' I mean how many elements come after the first address pointed to by 'str'.

2. Single quotes means a single character, double quotes is short-hand for an array of single characters -- nul terminated,

Code:

char hello[] = "hello";

Is the same as

Code:

char hello[] = {'h', 'e', 'l', 'l', 'o', '\0'};

3. They're really blue-prints, it's far more convenient to use a blue-print to build something than start from scratch every time.

For example, if you wanted 2 x's, y's, z's in main(),

Code:

int main(void)
{
    int x1, x2, y1, y2, z1, z2;
    x1 = 5;
    x2 = 10;
    y1 = 60;
    y2 = 50;
    z1 = 9;
    z2 = 18;
    return 0;
}

Hence repeat for n variables.
It's far easier to write,

Code:

struct num_t
{
    int x, y, z;
};

int main(void)
{
    struct num_t one, two;
    one.x = 5;
    one.y = 60;
    one.z = 9;
    two.x = 10;
    two.y = 50;
    two.z = 18;
    return 0;
}

See how only 2 variables compared to 6 were declared in main().

You can then pass the structures to other functions without worrying about what's inside. It turns out to be less typing.

The key on structures is that they hold a collection of items - such as a rectangle can be defined as x, y, width, height, so you make a struct:

Code:

struct rect
{ 
   int x;
   int y;
   int width;
   int length;
};

Of course, it's possible to just use 4 variables each time you want to represent a rectangle. But say you wanted to represent 10 rectangles in an array:

Code:

int x[10];
int y[10];
int width[10];
int length[10]

could be used, but isn't it clearer that we have 10 RECTANGLES (rather than some arbitrary set of integer arrays) if we write this:

Code:

struct rect rectangles[10];

Also, when passing arguments to functions, structures help, because there is only one parameter, instead of several:

Code:

void drawRectangle(struct rect r, int colour)
{
    MoveTo(r.x, r.y);
    LineTo(r.x+r.width, r.y);
    LineTo(r.x+r.width, r.y + r.height);
    LineTo(r.x, r.y + r.height);
    LineTo(r.x, r.y);
}

--
Mats

Originally Posted by CodeGeek20

I have three questions here. First, function prototypes such as

Code:

 void strip_newline(char *str, int size) {}

appeared out of nowhere, so this is my question about that: What does the * mean, and how does it know that int size is the size of an array?

Second, in the code used, for that function, the newline and null characters are enclsed in ' ' rather than " ". Why is that?

Third, structures. They seem to just be more to type. Struct.x = 1 instead of just x = 1. Why not just declare the variables inside main()?

Thanks!
CG-20

I'm going to answer in metahpors today:
1. If I give you a lemon and a lemon squeezer, how do I know you're going to squeeze me some lemon juice? The answer is of course that I don't know that, but it would be the most sensible thing for a person to do with those items. You could of course do whatever you wanted with them though.

2. This has been answered.

3. Which would you rather have: Ten boxes of 500-piece jigsaw puzzles, or 5000 assorted jigsaw puzzle pieces all of which belong to one of ten puzzles?