为什么浮动取0.699999而不是0.7 [英] Why float taking 0.699999 instead of 0.7

问题描述

这里，x取0.699999而不是0.7，但y取分配的0.5。你能告诉我这种行为的确切原因是什么。

Here x is taking 0.699999 instead of 0.7 but y is taking 0.5 as assigned. Can you tell me what is the exact reason for this behavior.

#include<iostream>
using namespace std;

int main()
{
float x = 0.7;
float y = 0.5;
if (x < 0.7)
{
if (y < 0.5)
   cout<<"2 is right"<<endl;
else 
   cout<<"1 is right"<<endl;
}
else 
   cout<<"0 is right"<<endl; 

cin.get();
return 0;
}

推荐答案

关于IEEE浮点的互联网。

There are lots of things on the internet about IEEE floating point.

0.5 = 1/2

所以可以写成两个权力的总和。

so can be written exactly as a sum of powers of two

0.7 = 7/10 = 1/2 + 1/5 = 1/2 + 1/8 + a bit more... etc

位更多永远不能完全是一个二的幂，所以你得到最近的它可以管理。

The bit more can never be exactly a power of two, so you get the closest it can manage.

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