Visual Studio的LNK2019错误-无法解析的外部符号

我是一个初学者，遇到上述错误。以下是来自三个文件的完整代码ball.h：

#ifndef BALL_H
#define BALL_H
namespace
{
    inline constexpr double gravity{ 9.81 };
}
    double getInitialHeight(void);
    double calculateHeight(double, int);
    void printHeight(double, int);
    void calculateAndPrintHeight(double, int);
    void solve(void);

#endif

ball.cpp：

#include "ball.h"
#include <iostream>

double getInitialHeight()
{
    std::cout << "Enter the height of the tower in meters ";
    double initialHeight{};
    std::cin >> initialHeight;
    return initialHeight;
}

double calculateHeight(double initialHeight, int secondsPassed)
{
    double distanceFallen{ BALL_H::gravity * secondsPassed * secondsPassed / 2.0 };
    double currentHeight{ initialHeight - distanceFallen };
    return currentHeight;
}

void printHeight(double height, int secondsPassed)
{
    if (height > 0.0)
    {
        std::cout << "At " << secondsPassed << " seconds, the ball is at height\t" << height << " meters.\n";
    }
    else
    {
        std::cout << "At " << secondsPassed << " seconds, the ball is on the ground.\n";
        std::exit(0);
    }


}

void calculateAndPrintHeight(double initialHeight, int secondsPassed)
{
    double height{ calculateHeight(initialHeight, secondsPassed) };
    printHeight(height, secondsPassed);
}

void solve()
{
    const double initialHeight{ getInitialHeight() };
    int secondsPassed{ 0 };
    while (true)
    {
        calculateAndPrintHeight(initialHeight, secondsPassed);
        secondsPassed++;
    }
}

Solution.cpp（解决方案中的主项目文件）：

#include <iostream>
#include "ball.h"

int main()
{
    solve();
    return 0;
}

我知道此问题是由于链接器找不到对的引用引起的solve()。但是，我不确定如何解决该问题。一种简单的解决方案是仅包含ball.cpp而不是ball.h：

#include <iostream>
#include "ball.cpp"

int main()
{
    solve();
    return 0;
}

这段代码有效，但是我想知道如何使用标头，因为我不确定这是否是一个好习惯。

编辑：这是错误列表：