简单的Perl For循环 [英] Simple Perl For-Loop

问题描述

我有一个for循环，我想每次增加0.1的变量，但是这个值的变化与增量不同，我不确定为什么。

我已经简化了for循环，它仍然给出了一个奇怪的输出：

$ p $ for（my $ t = 1000; $ t < 1500; $ t + = 0.1）{
print$ t \\\
;



$ b $ p





  1034.9 
 1035 
 1035.1 
 1035.2 
 1035.3 
 1035.4 
 1035.49999999999 
 1035.59999999999 
 1035.69999999999 
 1035.79999999999 
 1035.89999999999 
 1035.99999999999 
 1036.09999999999 
 1036.19999999999 
 1036.29999999999 
 [然后就这样到1500] 
  

我不知道小数点在哪里。这是一个问题，我对Perl的理解？

提前致谢。

解决方案

  $ perl -e'printf％.20g\\\
， 0.1'
 0.10000000000000001 
  

不要将浮点数与另一个浮点数进行比较，注意错误的累积。

这里简单的解决方法是使用整数进行算术运算，并在需要时生成浮点数字

pre $ for（my $ tx10 = 10000; $ tx10 <15000; ++ $ tx10）{
my $ t = $ tx10 / 10;
打印$ t \\\
;







简化为



 为我的$ tx10（10000..14999）{
 my $ t = $ tx10 / 10; 
打印$ t \\\
; 
 
 $ / code> 





---

  ____ ____ ____ 
 0.1 = 0.00011 0.4 = 0.0110 0.7 = 0.10110 
 ____ ____ 
 0.2 = 0.0011 0.5 = 0.1 0.8 = 0.11001 
 ____ ____ ____ 
 0.3 = 0.01001 0.6 = 0.1001 0.9 = 0.11100 
  

I have a for loop and I want to increment the variable by 0.1 each time, however the value changes differently from the increment and I am unsure as to why.

I've simplified the for loop and it still gives a strange output:

for (my $t = 1000; $t < 1500 ;$t+=0.1) {
print "$t\n";
}

It prints:

1034.9
1035
1035.1
1035.2
1035.3
1035.4
1035.49999999999
1035.59999999999
1035.69999999999
1035.79999999999
1035.89999999999
1035.99999999999
1036.09999999999
1036.19999999999
1036.29999999999
[it then goes on like this to 1500]

I do not know where the decimal places are coming from. Is this a problem with my understanding of Perl?

Thanks in advance.

解决方案

1/10 is a periodic number in binary like 1/3 is in decimal. It cannot be represented exactly as a floating point number.

$ perl -e'printf "%.20g\n", 0.1'
0.10000000000000001

Never compare a floating pointer number to another without involving a tolerance, and be wary of accumulation of error.

The simple solution here to to do the arithmetic using integers, and generate the floating point numbers when needed

for (my $tx10 = 10000; $tx10 < 15000; ++$tx10) {
   my $t = $tx10/10;
   print "$t\n";
}

which simplifies to

for my $tx10 (10000..14999) {
   my $t = $tx10/10;
   print "$t\n";
}

---

         ____            ____             ____
0.1 = 0.00011    0.4 = 0.0110    0.7 = 0.10110
        ____                              ____
0.2 = 0.0011     0.5 = 0.1       0.8 = 0.11001
         ____            ____             ____
0.3 = 0.01001    0.6 = 0.1001    0.9 = 0.11100

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