c++ - 简单函数的问题

Question

我正在编写代码来调用与力、质量和加速度方程有关的函数。函数被正确调用，但输入未按应有的方式相乘。我对第一个函数的输出是一个非常小的数字，第一个函数的输出始终为 0。这是我的代码。任何反馈都会非常有帮助。谢谢。

#include <iostream>
#include <cstdlib>

using namespace std;

void displayMenu();
double force(double);
double secondForce(double,double);

int main(int argc, char** argv) 
{
    int menuOption;
    displayMenu();
    system("PAUSE");
    return 0;
}

void displayMenu(void)
{
    int menuOption;
    double weight, accel;
    cout << "           Main Menu" << endl;
    cout << "Enter 1 for Force calculation with acceleration = 9.8m/s^2.\n";
    cout << "Enter 2 for Force calculation with user defined acceleration.\n";
    cout << "Enter 3 to quit the program.\n";
    cin >> menuOption;
        if(menuOption==1)
        {
            cout << "Enter a mass.\n";
            cin >> weight;
            cout << "The force is ";
            cout << force(weight);  
            cout << "N.";
            }
        else if(menuOption==2){
            cout << "Enter a mass.\n";
            cin >> weight;
            cout << "Enter an acceleration.\n";
            cin >> accel;
            cout << "The force is ";
            cout << secondForce(weight, accel);
            cout << "N.";
        }
}

double force(double weight)
{
    double force, mass;
    force=(mass*(9.8));
    return force;
}

double secondForce(double secondMass, double secondWeight)
{
    double secondForce, mass, acceleration;
    secondForce=(mass*acceleration);
    return secondForce;

}

Answer 1

您在函数中使用了未初始化的变量。在你的程序中使用这些未初始化的变量是 undefined behavior .

force=(mass*(9.8)); << mass has a garbage value
secondForce=(mass*acceleration); << mass and acceleration have a garbage value

我想你是想拥有

double force(double weight)
{
    return weight * 9.8;
}

double secondForce(double secondMass, double secondAccel)
{
   return secondMAss * secondAccel;
}