write a function to round off numbers

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Zcarfaz
Zcarfaz 2014-2-28
评论： Image Analyst 2014-2-28
Write your own roundn function that takes a floating point value as its input and rounds its nth decimal digit to the nearest number.
>> res = roundn(5.672,3); % results in res = 5.67
>> res = roundn(5.677,3); % results in res = 5.68
>> res = roundn(-5.672,3); % results in res = -5.67
>> res = roundn(-5.677,3); % results in res = -5.68

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回答（2 个）

Image Analyst
Image Analyst 2014-2-28
Try multiplying by a factor of 10 then rounding and dividing. That should be a good hint - probably too much of one.
  2 个评论
Zcarfaz
Zcarfaz 2014-2-28
ok I got this for but when i run the function it won't give the right answer but when I do it manually on the command window it works. also this is not the way i have to do it I need to write a for loop to check the value of the myfloat and then change the factor of 10 accordingly. please help. thanks!
function output = roundn(myinput,myfloat)
if myfloat == 1
output = round(myinput*10)/10;
fprintf('%.1f\n', output);
end
if myfloat == 2
output = round(myinput*100)/100;
fprintf('%.2f\n', output);
end
if myfloat == 3
output = round(myinput*1000)/1000;
fprintf('%.3f\n', output);
end
end
Image Analyst
Image Analyst 2014-2-28
Instead of checking for every possible factor of 10, why don't you just use 10^myFloat?
And how are you running it, if not from the command line? What value are you passing in when it does not run?

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Walter Roberson
Walter Roberson 2014-2-28
This cannot be done in MATLAB, not if the values are to be stored numerically as datatype single() or double().
>> fprintf('%.999g\n', 0.1)
0.1000000000000000055511151231257827021181583404541015625
This establishes that even if you had 0.1 already given, that you do not actually get exactly 0.1 stored.

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