冲突的类型和先前的 x 声明在这里......什么？

当我有时间的时候，我已经自学了几个月的 C 语言，但我遇到了一个我不知道如何解决的问题。

具体来说，当我尝试使用 gcc 编译它时，我得到：

geometry.c:8: error: conflicting types for ‘trapezoid’
geometry.c:7: note: previous declaration of ‘trapezoid’ was here
geometry.c:48: error: conflicting types for ‘trapezoid’
geometry.c:7: note: previous declaration of ‘trapezoid’ was here
geometry.c:119: error: conflicting types for ‘trapezoid_area’
geometry.c:59: note: previous implicit declaration of ‘trapezoid_area’ was here
geometry.c: In function ‘cone_volume’:
geometry.c:128: error: called object ‘3.14100000000000001421085471520200371742248535156e+0’ is not a function
geometry.c: In function ‘cylinder_volume’:
geometry.c:136: error: called object ‘3.14100000000000001421085471520200371742248535156e+0’ is not a function
  

现在，我想我可能需要对函数进行类型转换，但我再次不确定。

看起来它想要将 PI（我将其定义为 3.141）读取为函数。有没有办法可以避免使用幻数 3.141（尽管它比其他幻数要少得多）？

//Geometric formulae
#include <stdio.h>
#include <math.h>

#define PI 3.141

float trapezoid(float b1, float b2, float h);
int trapezoid();
float sphere_volume(float r);
int sphere();
float cone_volume(float r, float h);
int cone();
float pyramid_volume(float b, float h);
int pyramid();
float cylinder_volume(float r, float h);
int cylinder();

int main(void) {
        char selection = 0;

        while(selection != 'q') {
                printf("\t--Geometric Formulas--\n");
                printf("\tSelection an option from the menu: ");
                scanf("%c", & selection);
                switch(selection) {
                        case 1: //Trapezoid area
                                printf("%d", trapezoid());
                                break;
                        case 2: //Sphere volume
                                printf("%d", sphere());
                                break;
                        case 3: //Cone volume
                                printf("%d", cone());
                                break;
                        case 4: //Pyramid volume
                                printf("%d", pyramid());
                                break;
                        case 5: //Cylinder volume
                                printf("%d", cylinder());
                                break;
                        default:
                                break;
                }
        }
}
//      --Shape Menus--
//Trapezoid
int trapezoid() {
        float h = 0, b1 = 0, b2 = 0;
        float traparea;

        printf("\tTrapezoid base 1: ");
        scanf("%3f", &b1);
        printf("\tTrapezoid base 2: ");
        scanf("%3f", &b2);
        printf("\tTrapezoid height: ");
        scanf("%3f", &b2);

        traparea = trapezoid_area(b1, b2, h);

        printf("\tTrapezoid Area: %3f\n", traparea); }

//Sphere
int sphere() {
        float r = 0;
        float spherevol;

        printf("\tSphere radius: ");
        scanf("%f", &r);

        spherevol = sphere_volume(r);

        printf("\tSphere volume: %3f\n", spherevol); }

//Cone
int cone() {
        float r = 0, h = 0;
        float conevol;

        printf("\tCone radius: ");
        scanf("%f", &r);
        printf("\tCone height: ");
        scanf("%f", &h);

        conevol = cone_volume(r, h);

        printf("\tCone volume: %3f\n", conevol); }

//Pyramid
int pyramid() {
        float b = 0, h = 0;
        float pyramidvol;

        printf("\tPyramid base: ");
        scanf("%f", &b);
        printf("\tPyramid height: ");
        scanf("%f", &h);

        pyramidvol = pyramid_volume(b, h);

        printf("\tPyramid volume: %3f\n", pyramidvol); }

//Cylinder
int cylinder() {
        float r = 0, h = 0;
        float cylindervol;

        printf("\tCylinder radius: ");
        scanf("%f", &r);
        printf("\tCylinder height: ");
        scanf("%f", &h);

        cylindervol = cylinder_volume(r, h);

        printf("Cylinder volume: %3f", cylindervol); }

//      --Geometric Formulas--
//Trapezoid Area Computation
float trapezoid_area(float b1, float b2, float h) {
        return ((b1 + b2) * h) / 2; }

//Sphere Volume Computation
float sphere_volume(float r) {
        return ((pow(r,3)) * (4 * PI)) / 3; }

//Cone Volume Computatioin
float cone_volume(float r, float h) {
        return ((PI(pow(r,2)) * h)) / 3; }

//Pyramid Volume Computation
float pyramid_volume(float b, float h) {
        return (b * h) / 3; }

//Cylinder Volume Computation
float cylinder_volume(float r, float h) {
        return (PI(pow(r,2))) * h; }

他们中的任何人都说存在“隐式”定义：这可以通过预先声明来解决。例如，您预先声明了浮动梯形 and 整型梯形，但你没有预先声明梯形面积。正如其他人指出的那样，您也不能像在 C++ 中那样在 C 中重载。

在某些领域，您尝试进行隐式乘法——例如，PI(幂(r,2))应该PI * (pow(r,2)).