Problem with working precision

Question

I have tried to resolve the problem of the following link How can I solve precision problem

I can tell the problem described in that link shortly here, It's no mater how many precision is there after decimal(.) the result should be 2 or 3 precision after decimal as per user requirement.e.g

N[10/3]
3

Output should be as per user wish precision as 2.

3.33
3.00

There I found NumberForm[] function as a solution, since the NumberForm[] function is wrap up the result, I can't get the result as number out of it.

I tried like this

NumberForm[N[10/3],{4,2}]
NumberForm[3, {4, 2}]

Output am getting is

3.33
3.00

But when I try to do further operation, it's not computing

NumberForm[N[10/3], {4, 2}] + 1
NumberForm[3, {4, 2}] + 1

Output

1+3.33
1+3.00

I tried other way also which follows

ToExpression[ToString[NumberForm[3, {4, 2}]]]

OutPut

3.

but I need output as 3.00. Help me to find the solution.

Answer 1

Is SetAccuracy what you want?

a = N[10/3, {∞, 3}]

3.33

b = 3``3

3.00

a + 1

4.33

b + 1

4.00

394.985674``3

394.99

Please note Accuracy is a different concept from Precision.

Answer 2

Use the $PrePrint global parameter:

$PrePrint = If[MatchQ[#, _?NumericQ], NumberForm[#, {4, 2}], #] &;

Note: if you dont want the way rationals will be represented after setting the global variable (e.g. $3.00/4.00$) then use this instead

$PrePrint = If[MatchQ[#, Except[_Rational,_?NumericQ]], NumberForm[#, {4, 2}], #] &;

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Update:

if you just want it for the InputField command try this instead

InputField[Dynamic[ToString@NumberForm[b, {4, 2}]], String]