Question

每次此代码在UNIX中运行时，它都会挂起并显示一个没有提示的新行。它编译没有错误。有谁知道这里有什么？

/*
This program uses a Monte Carlo simulation to maximize widget profits.
 */

#include <stdio.h>
#include <stdlib.h>

// constant values used in the simulation
#define MIN_WIDGETS 1000 // minimum widgets per month
#define MAX_WIDGETS 1500 // maximum widgets per month

#define MIN_COST 0.25 // minimum cost per widget
#define MAX_COST 0.82 // maximum cost per widget

#define MIN_CONVERSION 0.01 // minimum converstion rate
#define MAX_CONVERSION 0.05 // maximum converstion rate

#define MIN_PROFIT 38 // minimum profit per sale
#define MAX_PROFIT 43 // maximum profit per sale

#define FIXED_OVERHEAD 400 // fixed overhead cost

#define NUM_SIMULATIONS 100 // number of simulations performed

void main()
{

  // to keep track of inputs in highest-profit simulation
  int bestW = 0; // widgets per month
  float bestC = 0; // cost per widget
  float bestR = 0; // rate of converstion
  float bestP = 0; // profit per sale
  float bestProfit = 0; // highest profit

  srand(time(0)); // initialize the random number generator
  float h = FIXED_OVERHEAD;

  int i; // loop index 
  for(i = 0; i < NUM_SIMULATIONS; i++)
    {
        // initialize inputs for this individual simulation
        int w = 0; // quantity of widgets bought
        float c = 0; // cost of a widget
        float r = 0; // conversion rate
        float p = 0; // profit per sale
        float profit = 0; // profit

        // simulate quantity of widgets bought per month, between MIN_WIDGETS and MAX_WIDGETS
        w = random() % (MAX_WIDGETS + 1); // to set the maximum value of w at MAX_WIDGETS
        while (w < MIN_WIDGETS) {
            w = random() % (MAX_WIDGETS + 1); // fetch new random number that may fit parameters
        }

        // simulate cost per widget, between MIN_COST and MAX_COST
        c = random() % 100; // to convert random number into an integer between 0 and 99
        while (c < (MIN_COST*100) || c > (MAX_COST*100)) {
            c = random() % 100; // fetch new random number that may fit parameters
        }
        c = c / 100.0; // convert cost back from cents into dollars

        // simulate conversion rate, between MIN_CONVERSION and MAX_CONVERSION
        r = random() % 100; // to convert random number into an integer between 0 and 99
        while (r < (MIN_CONVERSION*100) || r > (MAX_CONVERSION*100)) {
            r = random() % 100; // fetch new random number that may fit parameters
        }
        r = r / 10.0; // convert back into fraction

        // simulate profit per sale, between MIN_PROFIT and MAX_PROFIT
        p = random() % ((MAX_PROFIT + 1)*100); // to convert random number into an integer between 0 and 4300
        while (p < MIN_PROFIT*100) {
            p = random() % (MAX_PROFIT + 1); // fetch new random number that may fit parameters
        }
        p = p / 100.0; // convert back into floating point with two decimal places after period

        profit = (w * r * p) - (h + c * w);

        printf("Current profit is $%.2f, with %d widgets at a %.2f cost per widget with a %.1f conversion rate and %.2f profit/sale.\n",
            profit, w, c, r, p);

        if (profit > bestProfit) {
            bestW = w;
            bestC = c;
            bestR = r;
            bestP = p;
            bestProfit = profit;
        }

    }

  printf("Maximum profit is $%.2f, with %d widgets at a %.2f cost per widget with a %.1f conversion rate and %.2f profit/sale.\n",
    bestProfit, bestW, bestC, bestR, bestP);

}

Answer 1

我认为错误就在这里：

while (p < MIN_PROFIT*100) {
    p = random() % (MAX_PROFIT + 1); // fetch new random number that may fit parameters
}

如果输入循环体，p将设置为0到MAX_PROFIT（= 43）之间的数字。它永远不会大于或等于MIN_PROFIT*100（= 3800），因此它将进入无限循环。

作为旁注，您可能需要考虑在此处使用do { } while循环，而不是使用while循环并将循环体写入两次。编写代码两次是一种很好的错误方法，因为当你改变其中一个实现时，你总是要记住改变另一个。如果您忘记更新两者，则会引入错误。这似乎就是这里发生的事情。

Answer 2

很难从代码墙中分辨出来，但它要么花费的时间比你想象的要长，要么你的许多时间之一是不正确的。

您可以替换while语句并通过获取介于0和各种最小和最大参数之间的差异的随机数，然后将其添加到min参数，而不是当前正在执行的操作来加快整个过程的速度。获取最大参数值的随机数，然后再次尝试，如果低于你的最小值。例如，对于小部件，您将丢弃2/3的结果。

短节目挂在C中

2 个答案: