XY平面中点的计算

Question

#include <stdio.h>

int main(double x, double y, double x1, double y1, double x2, double y2)
{
    // First corner (botton left) of the rectangle
    printf("Choose x and y for the first corner that the rectangle should start:\n");
    scanf("%lf%lf", &x1, &y1);

    // Opposite corner(top right) that should make the rectangle possible 
    printf("Choose x and y for the first corner that the rectangle should end:\n");
    scanf("%lf%lf", &x2, &y2);

    // The position of the point that should be checked
    printf("Choose the x and y that should be checked:\n");
    scanf("%lf%lf", &x, &y);
    if (x1 < x < x2 && y1 < y < y2)
    {
        return 5;
    }
    else if (x1 == x && x == x2 && y1 == y && y == y2)
    {
        return 3;
    }
    else
    {
        return 0;
    }

    system("pause");

}

I have got a small problem with the calculation.

I'm trying to make the program tell me if one point is inside the rectangle, on the edge or outside but I always get the result as 5 even though it's not inside the rectangle.

Also, I am not sure if I have missed to mention the "double x, double y,..." somewhere or if I only should write like I did the scanf statment?

Answer 1

You should try to replace this test

if (x1 < x < x2 && y1 < y < y2)

with

if (x1 < x && x < x2 && y1 < y && y < y2)

Regarding your 2nd test, it will never be true unless x1=x2 and y1=y2, ie your rectangle actually is a point. Replace with

else if ( (x1 == x || x == x2) && (y1 == y || y == y2))

Answer 2

Various problems

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• As @StephaneM identified, the x1 < x < x2 is incorrect.

   // if (x1 < x < x2 && y1 < y < y2) if (x1 < x && x < x2 && y1 < y && y < y2) 

x1 < x < x2 tests if x1 < x , which results in 0 or 1. Then 0_or_1 < x2 is tested. Not what OP needs.

---

• Unusual and certainly incorrect main() function signature

Define the double variables after the function header.

// int main(double x, double y, double x1, double y1, double x2, double y2) {
int main(void) {
  double x, y, x1, y1, x2, y2;

---

• Incorrect "on the edge" test

x1 == x && x == x2 && y1 == y && y == y2 is only true when the rectangle and point are all a single point.

Instead, take advantage that the point is not inside.

if (x1 < x && x < x2 && y1 < y && y < y2) {
    return 5; // inside
} else if (x1 <= x && x <= x2 && y1 <= y && y <= y2) {  // include = in each compare
    return 3; // on edge
} else {
    return 0; // outside
}

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Code may also want to exchange x1,x2 should x2 < x1 . Same for y1,y2 .