[英]Beginner C++ - Simple random walk program with a strange setw bug
I've been tasked with creating a very simple random walk program for a C++ class. 我的任务是为C ++类创建一个非常简单的随机游走程序。 I wrote it and was fairly sure everything was correct but I am getting this strange bug.
我写了它,并确定一切都正确,但是我遇到了这个奇怪的错误。 From 0 to 10 the steps line up even though the coordinates show that its taking alternating left and right steps.
即使坐标显示其从左到右交替走动,步长也会从0到10排列。
#include<iostream>
#include<iomanip>
#include<cmath>
using namespace std;
int main()
{
int steps,i,pos=10;
srand(13699);
cout << "Please enter the amount of steps to be taken: ";
cin >> steps;
cout << endl;
for (i=0;i<=steps;i++)
{
if (rand()%2)
pos+=1;
else
pos-=1;
cout << i << ": " << pos-10 << ": " << setw(pos) << "*" << endl;
}
} // main
There is very obviously some sort of pattern here, but for the life of me I can't figure it out... Here is a link to a screenshot of the output if it helps. 很明显,这里有某种模式,但是对于我的一生,我无法弄清楚……如果有帮助,可以链接到输出屏幕截图。 http://i.stack.imgur.com/USx4U.png Thanks for any help y'all can give!
http://i.stack.imgur.com/USx4U.png谢谢大家的帮助!
The answer is not in the code but rather in your interpretation of the output. 答案不在于代码,而在于您对输出的解释。
When the pos-10 is less than 0 then the area where you print this value is longer (because of the minus sign), then your 'walker' is shifted right a position in the output. 当pos-10小于0时,则您打印此值的区域会更长(由于减号),因此您的“行者”会在输出中右移一个位置。
Similar reason when it goes from 9 to 10 it isn't right. 类似的原因,当它从9变为10时,它是不正确的。
Think about what it means that the colons on the left are not in a straight line. 考虑一下左边的冒号不是直线的意思。
The "lining up" for i
between 1 and 10 makes sense. i
在1到10之间的“排队”是有道理的。
Take the first two lines, for example: 以前两行为例:
i == 1
, you have pos == 10
, and the *
is printed 10 spaces after the :
. i == 1
,您的pos == 10
,并且*
在:
之后10个空格打印。 i == 2
, you have pos == 9
, and the *
is printed 9 spaces after the :
. i == 2
,您有pos == 9
,并且*
在:
之后打印9个空格。 But because you are printing 0
(one character) in the first line and -1
(two characters) in the second line, the *
end up on the same place in each line. 但是,因为您在第一行中打印
0
(一个字符),在第二行中打印-1
(两个字符),所以*
结束于每行的同一位置。
BTW, you are using the same value (13699) for seeding the RNG every time you run your program. 顺便说一句,您每次运行程序时都使用相同的值(13699)作为RNG的种子。
Try using a more "random" value, for example, a time-based one: 尝试使用更多的“随机”值,例如基于时间的值:
srand((unsigned int)time(NULL));
You'll need to #include <time.h>
in your source file. 您需要在源文件中
#include <time.h>
。
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