指向圆形结构的指针数组

Question

I have a array of 50 pointers that point to a circle struct that contains the x and y center coordinates, and the radius for a circle. I allocated all of the memory and used rand_float to create random x, y, and z for the circles. The point to my program is the find the circle with the largest area and print it out. I am experiencing problems with my program, I understand that with rand results will not be the same every time but my values are no where near the intended output. I am also not seeing the printf output from largestcircle in the output. Lastly I receive a error when I try running the program with free(circleptr ).

#include <stdio.h>
#include <stdlib.h>
#define PI 3.14
double rand_float(double a,double b){        //function provided my teacher.
    return ((double)rand()/RAND_MAX)*(b-a)+a;  
}
struct circle{
    double x;
    double y;
    double z;
};
 void largestcircle(struct circle **circleptr){
    float max = 0, radius =0, x= 0, y=0;
    int i;
    for(i = 0; i<50; i++){
        if(circleptr[i]->z *circleptr[i] ->z *PI > max){
            max = circleptr[i]->z*2*PI;
            radius = circleptr[i]->z;
            x = circleptr[i] ->x;
            y = circleptr[i] ->y;
        }
    }
    printf("Circle with largest area (%f) has center (%f, %f) and radius %f\n", max,x,y,radius);
}
int main(void) {
    struct circle *circleptr[50];
                             //dynamically allocate memory to store a circle
    int i;
    for(i=0; i<50; i++){
        circleptr[i] = (struct circle*)malloc(sizeof(struct circle));
    }
                             //randomly generate circles
    for(i=0; i<50; i++){//x
        circleptr[i]->x = rand_float(100, 900);
        circleptr[i]->y = rand_float(100, 900);
        circleptr[i]->z = rand_float(0, 100);
        //printf("%11f %11f %11f \n", circleptr[i] ->x, circleptr[i]->y, circleptr[i]->z);
    }
    largestcircle(circleptr);
    for(i=0; i<50; i++){
        free(circleptr[i]);
    }
    return 0;
}

the output should look something like:

Circle with largest area (31380.837301) has center (774.922941,897.436445) and radius 99.969481

My current xy and z values look like:

1885193628 -622124880 -622124884 
1885193628 -622124868 -622124872 
1885193628 -622124856 -622124860 
1885193628 -622124844 -622124848 
1885193628 -622124832 -622124836 
1885193628 -622124820 -622124824 
1885193628 -622124808 -622124812 
1885193628 -622124796 -622124800 
1885193628 -622124784 -622124788 
1885193628 -622124772 -622124776......etc.

Thoughts?

Answer 1

The problem where you are seeing some garbage random values for circle->x, y and z is is with your format specifier, while you are printing the circle->x , circle->y and circle->z . Use %f instead of %d since you are using double and not an int .

printf("%d %d %d \n", circleptr[i]->x, circleptr[i]->y, circleptr[i]->z);

Change above to

printf("%f %f %f \n", circleptr[i]->x, circleptr[i]->y, circleptr[i]->z);

Answer 2

Here is your problem, you re using %d , use %llf

printf("%llf %llf %llf \n", circleptr[i] ->x, circleptr[i]->y, circleptr[i]->z);
printf("Circle with largest area (%llf) has center (%llf, %llf) and radius %llf\n", max, x, y, radius);

also you have a bit missclick here I instead of i while free memory

Answer 3

There is a problem with this function:

 void largestcircle(struct circle **circleptr){
     float max = 0, radius =0, x= 0, y=0;
     int i;

     for(i = 0; i<50; i++){
         if(circleptr[i]->z *circleptr[i] ->z *PI > max){
             max = circleptr[i]->z*2*PI;
             radius = circleptr[i]->z;
             x = circleptr[i] ->x;
             y = circleptr[i] ->y;
         }
      }
      printf("Circle with largest area (%f) has center (%f, %f) and radius %f\n", max,x,y,radius);
  }

The if() statement compared for the area of a circle which is pie * r * r. But within if(), max is set to circumference of a circle which is 2 * pie * r.

This will give you the wrong answer.