How can decimals not be rounded

Question

Shuoze Xu 2022-6-16

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1741500-how-can-decimals-not-be-rounded

编辑： the cyclist 2022-6-16

采纳的回答： the cyclist

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Hi.

That is my code.

float_number = input('Please enter a float point number: ');
fprintf("The number is %.2f\n",float_number);

Sample test:

Please enter a float point number: 5.126

The number is 5.13

When the user enters a decimal, the result only keeps two decimal places, but I don't want the last decimal place to be rounded.

I don't want 5.13. I want 5.12.

How to do it?

Thank you.

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Answer 1

the cyclist 2022-6-16

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1741500-how-can-decimals-not-be-rounded#answer_986605

编辑：the cyclist 2022-6-16

在 MATLAB Online 中打开

Here is one way:

roundTo = 2; % Set this value
float_number = 5.126; % User's value
% Algorithm
roundToPower = 10^roundTo;
roundedDisp = floor(float_number*roundToPower)/roundToPower;
fprintf("The number is %.2f\n",roundedDisp);
The number is 5.12

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Stephen23 2022-6-16

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"I like to know more simple method."

Ultimately all numeric -> text conversion routines perform rounding, which is a good thing because it provides the most expected output from binary floating point numbers. For example:

x = 0.3
x = 0.3000
fprintf('%.40f\n',x)
0.2999999999999999888977697537484345957637

A naive "simple" approach might simply truncate this to 0.29, which is unlikely to be what the user expects.

The cyclist's approach is good, performing a few basic numeric operations is not complex.

Walter Roberson 2022-6-16

MATLAB does not provide any built-in function for this purpose.

For MacOS only (not sure if Linux was fixed yet), you can sprintf the number with a %.800g format, and do text manipulation on the result to get the number of decimal places you want.

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