Question

在我详细了解代码之前，让我解释一下这个问题。我使用Microsoft Visual Studio 2013编译和运行此代码。当我从计算概率的函数中为任何行添加书签时，此代码执行完美。但是，当我没有为任何行添加书签或为主函数中的某些行添加书签时，程序无法正常工作。通过不工作我的意思是无论我运行多少次，它都会将概率设为100％或0％。答案是50％，因此概率应该接近50％。（当我模拟它300次，同时书签它给了42％）似乎这个问题与内存有关。但我只是一名CS学生，所以我真的只是猜测这一点。任何类型的反馈或解决方案都表示赞赏。

让我解释代码假设要做什么。我的朋友最近问我一个概率问题。我无法使用某种类型的逻辑解决它，这使得它很容易解决。所以我决定制作一个小程序，通过模拟给定的时间来计算它的几率。所以这就是问题。

＆＃34;飞机上有100个座位。第一位乘客丢失了机票。他不知道哪个座位是他的。所以他随意坐着。这个人一个接一个地来到飞机后的每个人。如果他们的座位是空的，他们就坐在指定的座位上。如果他们的座位被占用，他们随意坐着。最后一个人坐在指定座位上的概率是多少？＆＃34;

以下是所有代码及其工作原理的评论。

#include <stdio.h>
#include <stdlib.h>
#include <iostream>
#include <iomanip>
#include <time.h>
#include <string.h>
#include <string>

#define PlaneCapacity 100                           //Plane capacity is now changeable. It helped me discover that this number is irrelevant to the answer of the question

using namespace std;

int PlacePeople(int SimNumber);

int SimNumber;
int Seat;
int PersonNo;
int SuccessNo = 0;
int Seats[PlaneCapacity];
int LatestSeat;

int main(){
    double Probability;
    cout << "Please enter the number of times you want the simulation to run:" << endl;
    cin >> SimNumber;
    PlacePeople(SimNumber);                         // Function that does the calculation
    Probability = (SuccessNo * 100) / (SimNumber);  //Calculate the probability in precentage form
    cout << "Probability: ";
    cout << Probability << endl;
    system("pause");
    return EXIT_SUCCESS;                            //Exit with success...I wish :(
}

int PlacePeople(int SimNumber){
    for (int a = 0; a < SimNumber; a++){            //Number of simulations. The code doesn't work when I bookmark this line
        Seats[PlaneCapacity] = { 0 };               //Array with elements that corresponds to the plane seats. Code works when I bookmark any line from this point onward. This line included.
        PersonNo = 1;                               //Last person that sit down
        LatestSeat = 0;                             //The seat the last person sit on
        srand(time(NULL));
        Seat = rand() % PlaneCapacity + 1;          //Randomizer that determines where the first passanger will sit
        if (Seat == 1){                             //If he sits in his place everything is golden!
            SuccessNo++;
        }
        if (1 < Seat && Seat < PlaneCapacity){      //If he doesn't sit in his place or the last passengers place things gets a bit messy
            Seats[Seat - 1] = PersonNo;             //Put him to his seat e.g 45th seat
            for (int b = 1; b < Seat - 1; b++){     //Everybody until that seat (43 people, from 2 to 44) sits in their regular place. 45th person has no where to sit :(
                PersonNo++;
                Seats[PersonNo - 1] = PersonNo;
            }
            PersonNo++;
            LatestSeat = PersonNo;
            while (PersonNo < PlaneCapacity){       //The same process for the first passanger will be repeated until the last person is seated

                Seat = rand() % (PlaneCapacity - LatestSeat + 1) + LatestSeat;      //I tried to lower the random number interval so the code would work a little more efficiently
                if (Seat == LatestSeat){                                            //The first guys seat might still be empty. So my interval is 1 bigger than it should be. Normally
                    SuccessNo++;                                                    //i would just place him when the random number says 1. But to make the interval shorter I now place the
                    break;                                                          //next guy to the first seat when the random number generator gives the latest seat number
                }                                                                   //So in my example if the random number is 45 I place the 45th guy to the 1st seat. Once the first seat is occupied
                Seats[Seat - 1] = PersonNo;                                         //We are guarenteed to have the last guy sit in his place so code can exit after that and increase the success counter
                for (int b = LatestSeat; b < Seat - 1; b++){
                    PersonNo++;
                    Seats[PersonNo - 1] = PersonNo;
                }
                PersonNo++;
                LatestSeat = PersonNo;
            }
        }
    }
    return SuccessNo;       //return the number of succesfull attepmts to the main function
}

谢谢你的时间！

Answer 1

要跟进我的评论，请在调用PlacePeople（）之前将srand调用移至main。当你没有进入调试器时，我认为该函数执行得足够快，所以外观的所有迭代都得到相同的随机数。要验证这一点，请尝试打印座位值，看看它是否随机分配在可用座位上。

C ++概率计算程序在Visual Studio中加入书签时有效，但在没有书签的情况下运行时不起作用

1 个答案: