1. ## need some help

I need some help with this programming project I am creating. The first two things I had to do I got just fine. The first two things were to compute the area of r and to compute the center of r, returning it as a point value. The next two thing I am having trouble with. Here's what I need help with:
1) Move r by x units in the x direction and y units in the y direction, returning the modified version of r. (x and y are additional arguments to the function.)
2) Determine whether a point p lies within r, returning TRUE or FALSE. (p is an additional argument of type struct point.)

I think I may have did the wrong thing for the second objective. I'm not sure. The complete direction was "compute the center of r, returning it as a point value." I don't think I used the point value and if anyone has any suggestions, please help. Here is the code I already have.

Code:
```#include <stdio.h>

struct point { int x, y;};
struct rectangle { struct point upper_left, lower_right;} r;

int area_of_r(struct rectangle rect);
float center_of_rx(struct rectangle rect);
float center_of_ry(struct rectangle rect);

int main() {

printf( "Input upper left corner of r : " );
scanf( "%d %d", &r.upper_left.x, &r.upper_left.y );

printf( "Input lower right corner of r : " );
scanf( "%d %d", &r.lower_right.x, &r.lower_right.y );
printf( "Area of r is %d\n", area_of_r(r) );

printf( "The center of r is ( %.2f, %.2f )\n", center_of_rx(r), center_of_ry(r));

return 0;

}

int area_of_r ( struct rectangle rect ) {
int area=0;

area = (rect.lower_right.x - rect.upper_left.x ) *
( rect.upper_left.y - rect.lower_right.y);

return area;
}

float center_of_rx(struct rectangle rect) {
float center=0;
center = (rect.lower_right.x - rect.lower_right.y)/2;

return center;
}

float center_of_ry(struct rectangle rect) {
float center=0;
center = (rect.upper_left.y - rect.upper_left.x)/2;

return center;
}```

2. Your code that determines the center point is wrong for a start. Surely the center x coordinate is the average of the upper left/bottom right x coordinates? ie (x1+x2)/2 and for y (y1+y2)/2, but your functions are (x2-y2)/2 and (y1-x1)/2 which makes little sense.

As for the question of determining if another point is in the rectangle, you just check if the x coord of the point is between the x coordinate of the left side and the right side, then you check if the y coord of the point is between the y coordinate of the top side and bottom side, simple.

3. Ok, I figured out how I messed up the second part and I fixed it where it returns a point value. So here's the new code:

Code:
```#include <stdio.h>

struct point { float x, y;} center;
struct rectangle { struct point upper_left, lower_right;} r;

float area_of_r(struct rectangle rect);
float center_of_r(struct rectangle rect);

int main() {

printf( "Input upper left corner of r : " );
scanf( "%f %f", &r.upper_left.x, &r.upper_left.y );

printf( "Input lower right corner of r : " );
scanf( "%f %f", &r.lower_right.x, &r.lower_right.y );
printf( "Area of r is %.2f\n", area_of_r(r) );
center_of_r(r);
printf( "The center of r is ( %.2f, %.2f )\n", center.x, center.y);

return 0;

}

float area_of_r ( struct rectangle rect ) {
float area=0;

area = (rect.lower_right.x - rect.upper_left.x ) *
( rect.upper_left.y - rect.lower_right.y);

return area;
}

float center_of_r(struct rectangle rect) {

center.x = (rect.upper_left.x + rect.lower_right.x)/2;
center.y = (rect.upper_left.y + rect.lower_right.y)/2;

}```

4. That code is still wrong, see my above post.

5. yea, sorry. I didn't notice the actual math part being wrong. I just knew that the center was supposed to use the structure point when being printed. Is this correct now? I edited above.

6. Looks okay.

It assumes that upper_left.x < lower_right.x and upper_left.y > lower_right.y in order to compute the area correctly, though. You could fix that with checking, or calculating the absolute value of the difference (the fabs function).

7. Ok, I have everything completed finally but I'm getting one last problem with the function. For some reason when it runs the 'p_evaluation' function, and I input the points to be tested equal to one of the points provided in 'upper_left' or 'lower_right' it returns FALSE. This is a point on the graph of the rectangle and it seems like my condition I have made would make this true. Any suggestions?

Code:
```#include <stdio.h>
#include <string.h>

struct point { float x, y;} center, units, p;
struct rectangle { struct point upper_left, lower_right;} r;

float area_of_r(struct rectangle rect);
float center_of_r(struct rectangle rect);
float move_units(struct rectangle rect);
int p_evaluation(struct rectangle rect);

int main() {
char condition[6];
int i;

printf( "Input upper left corner of r : " );
scanf( "%f %f", &r.upper_left.x, &r.upper_left.y );

printf( "Input lower right corner of r : " );
scanf( "%f %f", &r.lower_right.x, &r.lower_right.y );
printf( "Area of r is %.2f\n", area_of_r(r) );
center_of_r(r);
printf( "The center of r is ( %.2f, %.2f )\n", center.x, center.y);

move_units(r);
i = p_evaluation(r);
if(i == 1)
strcpy(condition, "TRUE");
else
strcpy(condition, "FALSE");

printf("\nThe point p evaluation returned: %s\n", condition);

return 0;

}

float area_of_r ( struct rectangle rect ) {
float area=0;

area = (rect.lower_right.x - rect.upper_left.x )*( rect.upper_left.y - rect.lower_right.y);

return area;
}

float center_of_r(struct rectangle rect) {

center.x = (rect.upper_left.x + rect.lower_right.x)/2;
center.y = (rect.upper_left.y + rect.lower_right.y)/2;

}

float move_units(struct rectangle rect) {

printf("Type the number of units to move the rectangle: ");
scanf("%f %f", &units.x, &units.y);
printf("\nThe modified points of the rectangle are: \nUpper left: ( %.2f, %.2f ) \nLower right: ( %.2f, %.2f)\n"
, rect.upper_left.x + units.x, rect.upper_left.y + units.y,
rect.lower_right.x + units.x, rect.lower_right.y + units.y);

}

int p_evaluation(struct rectangle rect) {
int i=0, j=1;

printf("Type a point to test if it is within the rectangle: ");
scanf("%f %f", &p.x, &p.y);

if(rect.upper_left.x <= p.x <= rect.lower_right.x && rect.upper_left.y >= p.y >= rect.lower_right.y)
return j;
else
return i;
}```

8. Although the expression x <= y <= z makes sense in maths, it won't do what you expect in C.

What it will do, is evaluate x <= y (and return 1 if true, 0 if false), and it will then take the result of that evaluation (1 or 0), and apply it to <= z. It will return the result of 1 <= z or 0 <=z as appropriate. This is clearly not what you want.

You need if (x <= y && y <= z) instead.

9. awesome, thanks for the help. I got it going good now.