Very simple 'if' statement with == operator not working

14 次查看（过去 30 天）
Graham
Graham 2017-12-22
评论： Star Strider 2017-12-22
I have some very basic logic that is not working. It's a simple 'if' statement with an '==' operator. Please help.
Program:
%simple_script.m
clear all
A = 0.40;
B = 0.20;
C = 0.60;
D = A + B;
if C == D
disp('It worked.')
else
disp('It did not work.')
end
Command Window:
>> simple_script
It did not work.
>>

请先登录，再回答此问题。

采纳的回答

Star Strider
Star Strider 2017-12-22
Welcome to the apparent inconsistencies of floating-point calculations. See the discussion in Why is 0.3 - 0.2 - 0.1 (or similar) not equal to zero? (link) for more informaiton.
Floating point approximations are similar in this regard to decimal 1/3 being approximated as 0.3333... Multiplying by 3 then gives 0.9999..., not 1.

更多回答（1 个）

Geoff Hayes
Geoff Hayes 2017-12-22
Graham - you are incorrectly trying to use equality with floating point numbers. See the Compare Floating-Point Numbers section of determine equality for an example of what to do.
Also, please see https://www.mathworks.com/matlabcentral/answers/267964-while-comparing-the-equality-of-two-floating-numbers-a-b-we-use-abs-a-b-tolerance-could-anyo and https://www.mathworks.com/matlabcentral/answers/57444-faq-why-is-0-3-0-2-0-1-not-equal-to-zero.

类别

在 Help Center 和 File Exchange 中查找有关 MATLAB 的更多信息

标签

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by