What does the line stand for

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January 23rd, 2013, 11:27 AM

ddeakpeti

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What does the line stand for

Hi everyone. I have a programe and I'm trying to understand what's going on... in one of the lines.

the code is the following:

Code:

int main()
{
    srand((unsigned) time(0));

	double PI = 3.14159265358979323846;

    point points[N], randompoint;
    int i = 0; 
	int j;

    //generate N different points
    while (i < N) {
        randompoint.x = (double) (rand() % XLIM);
        randompoint.y = (double) (rand() % YLIM);
        int exist = 0;
        for (j = 0; j < i; ++j)
            if (points[j].x == randompoint.x && points[j].y == randompoint.y) {
                exist = 1;
                break;
            }
        if (!exist) {
            points[i].x = randompoint.x;
            points[i].y = randompoint.y;
            ++i;
        }
    }

My question, is about the line: point points[N], randompoint;

What does it do? Or what kind of "thing" is it?
Maybe I should include the rest of the int main, let me know if this is not enough information.
Thanks in advance

January 23rd, 2013, 11:47 AM

swapy

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i think program is incomplete or u may have missed something..
point is a user defined datatype... it will be mostly a structure and its variables are x and y......

January 23rd, 2013, 11:52 AM

swapy

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what is xlim ylim... even some header file may be missing and N must have a value...

structure may look like this

struct p{
int x,y;
}point;

January 23rd, 2013, 11:59 AM

clifford

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Code:

point points[N], randompoint;

Declares two variables, an array of points and a single point. It is the same as:

Code:

point points[N] ;
point randompoint ;

but is written by terminally lazy coders.

January 23rd, 2013, 12:58 PM

dwise1_aol

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N, XLIM, and YLIM are undoubtedly macros created by #define statements; eg:

Code:

#define N 100
#define XLIM  42
#define YLIM  42

When you compile the program, first the pre-processor will scan through the source code and replace every occurance of a macro name with the string that it's defined as being; eg, assuming the example #define's above, this

Code:

    point points[N], randompoint;
    int i = 0; 
	int j;

    //generate N different points
    while (i < N) {
        randompoint.x = (double) (rand() % XLIM);
        randompoint.y = (double) (rand() % YLIM);

will become

Code:

    point points[100], randompoint;
    int i = 0; 
	int j;

    //generate N different points
    while (i < 100) {
        randompoint.x = (double) (rand() % 42);
        randompoint.y = (double) (rand() % 42);

Like the missing declaration of the struct point, those missing macro definitions are probably above main in the upper portion of the program that was not included.

BTW, it is common coding convention to write all macro names in all-caps, so that when reading the source code you can immediately recognize the macros. And since by this convention no other identifiers (variable, typedef, or function names) are written in all caps, that allows you to "reuse" those names. Therefore, while N is a macro, you can still use n as a variable name.

Comments on this post

swapy agrees!