同一个程序每次返回不同的输出？

Question

每次我运行程序时，使用完全相同的值（直径为 25，深度为 5），我得到不同的water_price值，我不知道为什么。

一些结果：

$6.62256e+07 is the total cost.
$0 is the total cost.
$2.43411e-27 is the total cost.

我不知道我是否正在处理 memory 中的值不能很好地相互配合，不冲洗或什么。

为什么每次运行此程序时结果都不同？

#include <iostream>

#define PI 3.1416
#define WATER_COST 1.80

using std::cout;
using std::cin;
using std::endl;

int main() {

    float pool_diameter, pool_depth;
    float pool_radius = pool_diameter / 2;
    float pool_volume_sq_inches = (PI * pool_radius * pool_radius * pool_depth) * 1728;
    float pool_gallons = pool_volume_sq_inches / 231;
    float water_price = (pool_gallons / 748) * WATER_COST;

    cout << "Enter the pool diameter: ";
    cin >> pool_diameter;
    cout << "\nEnter the pool depth: ";
    cin >> pool_depth;

    cout << "\n$" << water_price << " is the total cost." << endl;

    return 0;
}

Answer 1

看看我们需要如何开始声明变量，然后当您要求输入时，它将存储在这些变量中，然后您可以继续进行所需的计算。

#include <iostream>
#define PI 3.1416
#define WATER_COST 1.80

using std::cout;
using std::cin;
using std::endl;

int main() {

    float pool_diameter = 0.0;
    float pool_depth = 0.0;

    cout << "Enter the pool diameter: ";
    cin >> pool_diameter;
    cout << "\nEnter the pool depth: ";
    cin >> pool_depth;


    float pool_radius = pool_diameter / 2;
    float pool_volume_sq_inches = (PI * pool_radius * pool_radius * pool_depth) * 1728;
    float pool_gallons = pool_volume_sq_inches / 231;
    float water_price = (pool_gallons / 748) * WATER_COST;


    cout << "\n$" << water_price << " is the total cost." << endl;

    return 0;
}

Answer 2

您可能希望在声明后尽快获得输入。

        float pool_diameter, pool_depth;

        cout << "Enter the pool diameter: ";
        cin >> pool_diameter;
        cout << "\nEnter the pool depth: ";
        cin >> pool_depth;

Rest 代码将按原样工作。

一个好的做法是像Omid-CompSci在这里回答的那样初始化你的变量。

Answer 3

语句float pool_radius = pool_diameter / 2; 在cin >> pool_diameter; . 每次使用默认值（垃圾值）来计算pool_radius是不同运行中不同值的原因。

更改顺序。