c - 为什么我的两个计算函数都会出现 Unresolved external 系统错误(错误 LNK2019)？

Question

为什么我的两个计算函数都会出现 Unresolved external 系统错误(错误 LNK2019)？错误 6 错误 LNK2019:无法解析的外部符号 _CalculateAreaRec错误7错误LNK2019:引用了无法解析的外部符号_CalcCircleArea错误 8 错误 LNK1120:2 个无法解析的外部

#include <math.h> 
#include <stdio.h>
#define PI 3.14159
#define _CRT_SECURE_NO_WARNINGS    //to avoid scanf warning or error
/* Function prototype */
int CalculateAreaRec(int length, int width);
double CalcCircleArea(double radius);
int GetInt(void);
int main(void)
{
    //Declared varibles 
    double radius;
    int length;
    int width;
    int GetInt(void);
    {
        // this function gets an integer from the user and returns it
        // this function is called 3 times from main

        //Prompt for the radius of the circle.
        printf("Whats the radius of the circle \n");
        //Get the radius from the keyboard.
        scanf("%lf", &radius);
        //Display the radius and area of the circle onto the screen.
        printf(" The radius is %lf and the area is %.4f \n", radius, CalcCircleArea(radius));
        //Prompt for the length of a side
        printf("Whats  the length of a side of rectangle \n");
        //Get the length from the keyboard
        scanf("%d", &length, CalculateAreaRec(length, width));
        //Prompt for the width of a side
        printf("Whats length of the width \n");
        //Get the width from the keyboard
        scanf(" %d", &width, CalculateAreaRec(length, width));
        //Display the side length, width, and area of the rectangle onto the screen.
        printf(" The side length  is %d the width is %d and the  area of the rectangle is   %d \n ", length, width, CalculateAreaRec);
    }
    double CalcCircleArea(double radius);
    {
        //Calculate the area of the circle (use 3.14).
        return (PI * radius * radius);
    }
    int CalculateAreaRec(int length, int width);
    //takes two arguments (base and height of the triangle) and returns the area 
    {
        return (length*width);
        //takes one argument (radius of the circle) and returns the area
    }
}

Answer 1

C 不支持嵌套函数。他们都必须生活在最高层，彼此独立。

除此之外，您的 main 中似乎没有任何代码来调用其他函数。

您还错误地调用了 CalculateAreaRec。它不应该是 scanf 的参数，并且您需要在将其作为 printf 的参数调用时为其提供参数。