定義一個圓的結構體，給兩個圓的圓心和半徑分別賦值，判斷兩個圓的關系（相交、相切、相離、重合）。
#import <Foundation/Foundation.h>
typedef struct
{
    int x;
    int y;
    float r;
} Circle;

void compareCircle(Circle a,Circle b)
{
    float  rr = 0;
    if (a.x>=b.x)//比較點坐標大小，用大數減掉小數；
    {
        int xab = a.x - b.x;
        if (a.y>=b.y)
        {
            int yab = a.y - b.y;
            rr = fabs(sqrt(xab * xab + yab * yab));
        }else
        {
            int yab = b.y - a.y;
            rr = fabs(sqrt(xab * xab + yab * yab));
        }
    }else
    {
        int xab = b.x - a.x;
        if (a.y>=b.y)
        {
            int yab = a.y - b.y;
            rr = fabs(sqrt(xab * xab + yab * yab));
        }
        else
        {
            int yab = b.y - a.y;
            rr = fabs(sqrt(xab * xab + yab * yab));
        }
    }
    if (a.x == b.x && a.y == b.y)
    {
        printf("兩個圓重合\n");
    }else if (rr > a.r + b.r)
    {
        printf("兩個圓相離\n");
    }else if ((rr ==a.r-b.r)||(rr==b.r-a.r)||(rr=a.r+b.r))
    {
        printf("兩個圓相切\n");
    }else
    {
        printf("兩個圓相交\n");
    }
}
int main()
{
    Circle c1,c2;
    printf("輸入要比較的圓1的坐標及半徑：\n");
    scanf("%d%d%f",&c1.x,&c1.y,&c1.r);
    printf("輸入要比較的圓2的坐標及半徑：\n");
    scanf("%d%d%f",&c2.x,&c2.y,&c2.r);
    compareCircle(c1, c2);
    return 0;
}