Question

我正在编写一个游戏，其中计算机选择用户必须猜测的随机数。然后，用户选择计算机必须猜测的数字（他只是猜测一个数字）。问题是我在游戏的第二部分中使用的rand（）函数有时会提供新范围之外的数字。例如，如果新范围为低= 4且高= 10，则rand（）提供12，这是不正确的。我试图理解为什么这个错误，但我找不到它。我在Dev-C ++中写作。代码就在下面，然后是输出。谢谢你的帮助和时间。

#include<iostream>
#include<conio.h>
#include<stdlib.h>
#include<time.h>




using namespace std;

int main()
{
  int computer_guess, nbr, nbrguesses, count_user_guess=0, count_computer_guess=0; 
  char user_comparison;

  int  low=1, high=99;  //initialize low to the lower boundary and high to the higher     boundary

  srand(time(0));
  nbr=rand()% 99 + 1;  //computer chooses a random number between 1 and 99...

  do
  {
    cout << "guess a number now! " << endl;
    cin >> nbrguesses;     //user enters the number he guessed...
    if ( nbrguesses>nbr)
       cout << "too big" <<endl;
    else if ( nbrguesses<nbr)
       cout << "too small" << endl;
    else if ( nbrguesses==nbr)
       cout << " you found the correct number! " <<endl;

    count_user_guess++;  //count the number of guesses from the user
  }
  while (nbrguesses!=nbr);

  cout << "you tried " << count_user_guess <<" times to find the right number " <<      endl<<endl;

  cout << "----------------------------------------------------------------------" << endl;
  cout << "Now, the computer will guess your number " << endl;

  do
  {
    srand(time(0));
    computer_guess=rand()% high + low;    //computer guesses the number
    cout << "computer guess: " << computer_guess <<endl;
    cout << "is it the correct number?" << endl;
    cin >> user_comparison;     //if user enter 
    if (user_comparison=='>')  // character '>' it means the number guessed by computer is too big
    {
       cout << "too big" <<endl;
       high= computer_guess-1;   //high is given a new boundary 
       cout << "***Current value of high = " << high << " and low = " << low << endl;    //display current boundaries

    }
    else if ( user_comparison=='<')  //the number guessed by computer is too small
    { 
      cout << "too small" << endl;
      low= computer_guess+1;  //low is given a new boundary
      cout << "***Current value of low = " << low << " and high = " << high << endl;  //display current boundaries

    }
    else if ( user_comparison=='=')
       cout << "Computer found the correct number! " <<endl;

    count_computer_guess++;  //count number of guesses from computer
  }
  while (user_comparison!='=');

  cout << "The computer tried " << count_computer_guess <<" times to find the right number " << endl;

  cout << "The Game is over now, have a good day!" << endl;
  getch();

  return 0; 

}

//**************Output******************************************

guess a number now!
50
too big
guess a number now!
25
you found the correct number!
you tried 2 times to find the right number

----------------------------------------------------------------------
Now, the computer will guess your number
computer guess: 11
is it the correct number?
>
too big
***Current value of high = 10 and low = 1
computer guess: 3
is it the correct number?
<
too small
***Current value of low = 4 and high = 10
computer guess: 12
is it the correct number?

Answer 1

你必须替换

computer_guess=rand()% high + low;

通过

computer_guess=rand()%(high- low + 1) + low;

在你的例子中你有低= 4和高= 10.但是你想要一个0到6之间的随机数并且添加4.不是0到10之间的一个，从那以后你可以得到高达14的结果。如果你不想包括上限（间隔[低，高[而不是[低，高]）你必须省略括号中的+1。

<强>为什么

rand（）返回一个非常大的整数。我们希望在区间[a，b]中得到一个随机数。如果我们取rand（）％5，我们得到一个数字0,1,2,3或4，所以从区间[0,4]。通常，rand（）％C在区间[0，C-1]中给出一个随机数。

如果我们添加一个常数，例如Rand（）％C + D，间隔移位：[D，C-1 + D]。所以回到问题，我们希望区间为[a，b]。因此，我们希望a = D表示较低的键，C-1 + D = b表示较高的键。这我们可以转换为C = b-D + 1 = b-a + 1。所以我们想要使用rand（）％（b-a + 1）+ a。

希望这能解释一下事情是如何运作的。

Answer 2

你非常接近，但试试这个：

rand()%(high-low)+low;

Answer 3

srand(time(0));
computer_guess=rand()% high + low;    //computer guesses the number

首先，不要在循环中调用srand。只需在程序启动时调用一次。

其次，这种逻辑是错误的。它应该是：

computer_guess=low + (rand() % (high-low+1));

（这假设高和低是包容性的。也就是说，如果高是10而低是1，则1和10都是可接受的猜测。）

rand（）函数在C ++中无法正常工作

3 个答案: