Question

我目前正在尝试用c ++模拟弹性碰撞。我有一个名为Particle的结构，我用它来描述对象。

//Defining the particle structure
struct particle {
  double x;   // Position
  double p;   // Momentum
  double im;  // Inverse Mass
  double v;   // Velocity
  double T;   // Kinetic Energy
  double a;   // Radius of a Particle
};

我使用创建这些结构的数组。

particle AP[n+2];

我程序的一部分需要使用时间变量及其速度来增加每个结构的位置。

我正在使用此代码

void LeapForward(struct particle AP[],double tfc,int n)
{
  for(int cycle=0; cycle<n+2; cycle++)
    {
      double second;
      second=AP[cycle].x+tfc*AP[cycle].v;
      AP[cycle].x=second;
    }
}

但是，似乎数组未被修改，而是重新创建。我想知道是否有人知道为什么会这样，如果是的话如何解决这个问题。

我的完整代码可以在下面找到。任何帮助将不胜感激。

//This program will be about particle collsions 
#include <iostream>
#include <cmath>
#include <fstream>
using namespace std;

//Function for collision of particles
void Collision(struct particle AP[],int chosen);
void Assignment(struct particle AP[],int n);
void LeapForward(struct particle AP[], double tfc, int n);
void TimeForCollision(struct particle AP[],double tfc, int chosen, int n);

//Defining the particle structure
struct particle {
  double x;   // Position
  double p;   // Momentum
  double im;  // Inverse Mass
  double v;   // Velocity
  double T;   // Kinetic Energy
  double a;   // Radius of a Particle
};

//Variable Declaration
int n; //Number of particles
double tfc; //This is going to be the time to leap forward
int chosen; //Which particles are to collide

  //Main program 

  int main()
  {
    cout<<"How many particle do you want to model: ";
    cin>>n;
    particle AP[n+2];    

    //Assigning value to Particles
    Assignment(AP,n);    

    cout<<endl<<"Two walls have been placed at x=0 and 20"<<endl;
    //Assignment of Wall Data. 
    AP[0].im=0.000001,AP[n+1].im=0.000001;
    AP[0].x=0,AP[n+1].v=0;
    AP[0].x=0,AP[n+1].x=20;
    AP[0].a=0,AP[n+1].a=0;

  ofstream Port;
  Port.open ("Positions.txt");
    for(int model=0; model<2;model++)
      {
    //Time for next collision
    TimeForCollision(AP,tfc,chosen,n);
    LeapForward(AP,tfc,n);
    Collision(AP,chosen);
    for(int plot=0; plot<n+2;plot++)
      {
        Port<<AP[plot].x<<"\t";
          }
    Port<<endl;
      }
  }


void Collision(struct particle AP[],int chosen)
{
  double combinemass=1/AP[chosen].im+1/AP[chosen+1].im;
  double result1=(AP[chosen].v*(1/(AP[chosen].im)-1/(AP[chosen+1].im))+(2*AP[chosen+1].v*1/(AP[chosen+1].im)))/combinemass;
  double result2=(AP[chosen+1].v*(1/(AP[chosen+1].im)-1/(AP[chosen].im))+(2*AP[chosen].v*1/(AP[chosen].im)))/combinemass;
  AP[chosen].v=result1;
  AP[chosen+1].v=result2;
}

void Assignment(struct particle AP[],int n)
{
for(int cycle=1;cycle<=n;cycle++)
  {
    cout<<"Data Input for particle number "<<cycle<<endl;
    double mass;
    cout<<"What is the position of the particle : ";
    cin>>AP[cycle].x;
    cout<<"What is the mass of the particle : ";
    cin>>mass;
    AP[cycle].im=1/mass;
    cout<<"What is the velocity of the particle : ";
    cin>>AP[cycle].v;
    cout<<"What is the radius of the particle : ";
    cin>>AP[cycle].a;
    //Data calculation
    AP[cycle].p=AP[cycle].v*mass;
    AP[cycle].T=0.5*AP[cycle].v*mass*mass;
  }
}

void LeapForward(struct particle AP[],double tfc,int n)
{
  for(int cycle=0; cycle<n+2; cycle++)
    {
      double second;
      second=AP[cycle].x+tfc*AP[cycle].v;
      AP[cycle].x=second;
    }
}

void  TimeForCollision(struct particle AP[],double tfc, int chosen, int n)
{
 double balance=0;
 tfc=0;
  for(int cycle=0;cycle<n+1;cycle++)
    {
      double placeh=abs(((AP[cycle+1].x-AP[cycle+1].a)-(AP[cycle].x+AP[cycle].a)))/(AP[cycle].v-AP[cycle+1].v);
       if(placeh>tfc && placeh>0)
        {
      tfc=placeh;
      chosen=cycle;
        }
   }
   cout<<tfc<<endl;
}

Answer 1

这是因为当您调用函数时，您将创建结构的新实例并修改新创建的实例，该实例将在函数末尾删除。

将值作为参考传递，如下所示：

void LeapForward(struct particle *AP, double tfc, int n);

此外，在LeapForward函数中，您不需要创建临时双变量。你可以使用类似的东西：

AP[cycle].x += tfc * AP[cycle].v;

Live demo。

修改结构数组的值

1 个答案: