我刚开始学习 C 语言中的函数指针，并尝试编写程序，但似乎有问题，我不明白是什么？

Question

所以，我试图编写一个程序，要求用户输入图形的点来计算欧几里得距离，并将其用作半径来给出圆的面积。
这是我的代码：

/*You have to take four points(x1,y1,x2,y2) from the user and use it radius to find area of a circle. To find the distance between these points, you will use the Euclidean distance formula.*/
#include <stdio.h>
#include <math.h>
#define PI 3.14

float euclideanDistance(float x1, float x2, float y1, float y2)
{
    float ed = 0;
    ed = sqrt((x2 - x1) * (x2 - x1) + (y2 - y1) * (y2 - y1));
    return ed;
}
int areaOfCircle(float x1, float y1, float x2, float y2, float(ed)(float x1, float y1, float x2, float y2))
{
    return PI * (*ed)(x1, y1, x2, y2) * (*ed)(x1, y1, x2, y2);
//not sure if it's correct or not. No error squiggles.

}
int main()
{
    float x1, y1, x2, y2;
    float (*fptr)(float, float, float, float);
    fptr = euclideanDistance;
    printf("Enter the four points x1,y1,x2,y2 to calculate the Euclidean Distance.\n");
    printf("x1:");
    scanf("%f", &x1);
    printf("y1:");
    scanf("%f", &y1);
    printf("x2:");
    scanf("%f", &x2);
    printf("y2:");
    scanf("%f", &y2);
    ;
    printf("The euclidean distance is %f", fptr(x1, x2, y1, y2));

    printf("The area of the circle which has the above mentioned Euclidean Distance as it's radius is: %f", areaOfCircle(x1, x2, y1, y1, fptr(x1, y1, x2, y2))); //error in this printf.

    return 0;
}

这里有两个问题。
我不知道如何在 areaOfCircle 中使用函数 euclideanDistance 作为半径，其次是如何在我的主要函数中实现它。
对于第二个问题，在 VS Code 中，它向我显示了错误。

{"message": "argument of type "float" is incompatible with parameter of type "float (*)(float x1, float y1, float x2, float y2)""}

请解释我做错了什么并指导我。

Answer 1

问题是您基本上是重复呼叫 euclideanDistance。在 main 中，您执行 areaOfCircle(x1, x2, y1, y1, fptr(x1, y1, x2, y2))，然后在 areaOfCircle 中，您执行 (*ed)(x1, y1, x2, y2)。要传递函数指针，您只需像传递任何其他类型的指针一样传递它，而不是使用参数调用它。换句话说，将 areaOfCircle(x1, x2, y1, y1, fptr(x1, y1, x2, y2)) 更改为 areaOfCircle(x1, x2, y1, y1, fptr)。

我刚开始学习 C 语言中的函数指针，并尝试编写程序，但似乎有问题，我不明白是什么？

I have just started learning function pointers in C and and was trying to code a program but there seems to be a problem and I can't understand what?

c

function-pointers