Solved

Question on checking for the size of a float value

Posted on 2004-09-21
5
220 Views
Last Modified: 2010-04-15
Hello, i'm tyring too check if an float value that someone enters is correct and does not exceed a certain range. Right now I'm trying to use E, where represnts the exponent to a power of 10 and digits represents 1 or more juxtaposed numbers. E can be the lower case, "e". There can be no more than 7 digits in any floating points number excluding the exponent (the decimal point does not count as a digit) Exponents are restriced to range of -38 to 38.

This is what I have right now:

      else if(out == 3)
            {
                  int exponent_check = 0;
                  std::istringstream(Lexeme.substr((Lexeme.length())-2 ,Lexeme.length())) >> exponent_check;      
                  if(((exponent_check >= 38) || (exponent_check <= -38)) && 
                     ((Lexeme.find("e") == ((Lexeme.length())-3)) || (Lexeme.find("E") == ((Lexeme.length())-3)) ||
                      (Lexeme.find("e") == ((Lexeme.length())-4)) || (Lexeme.find("E") == ((Lexeme.length())-4))) && Lexeme.find(".") != 0)
                  {
                        cout << "\n*** ERROR - Float Literal exponent is out of range ( -38 < x < 38 )" << endl;
//                        num_bad_real_constants++;
                        return 40;
                  }

I'm trying to check the the length then compare. The number that I am checking is the following:

1.35562127e1

This number should be throwing an error but it doesn't so I need to know what I am doing wrong in the check. Any help with this would be great.
0
Comment
Question by:DancingFighterG
5 Comments
 
LVL 55

Expert Comment

by:Jaime Olivares
ID: 12118365
You can use logaritms. Decimal logarithms tells you the exponent of a floating number.
Make some tests with log() function.
Remember to #include "math.h" header file.



 
0
 
LVL 45

Expert Comment

by:sunnycoder
ID: 12120048
Hi DancingFighterG,

Perhaps you should have this question in the C++ TA. I can give you a C solution if you want. Alernatively, I can move this question to C++ TA. Since some experts visit both C and C++ TAs, may beyou can wait a while before they see and comment on this.

sunnycoder
0
 
LVL 8

Expert Comment

by:ssnkumar
ID: 12121297
Your exponent is within the range. That's why it is not throwing error.
But, I have got one suggestion for you: Divide your condition statement to different if statements. And don't do the calculation inside a condition statement. Make it as simple as possible. Then it will be easier to debug and understand and errors will be lesser.

-ssnkumar
0
 
LVL 22

Assisted Solution

by:grg99
grg99 earned 25 total points
ID: 12126429
Your parsing is a bit loose, what will your code do with the perfectly valid numbers:

1.0e+38

1.0e0000000000038

I'd suggest this approach:

(0) Get a leading plus or minus, if not found, assume plus.
(1) Get a digit string, if none found, error out.
(2) If there's a dot, get another digit string, if not found, assume .00000
    (2a) get a letter, if it's 'E' or 'e':
           (2a.a)  get a sign, if not foiund. assume plus.
           (2.a.b) get a digit string, if not found, error out.

------------------
That's a much more bulletproof way to parse a real constant.

 
0
 
LVL 9

Accepted Solution

by:
jhshukla earned 25 total points
ID: 12129428
addendum to grg99's suggestion:

(0) Get a leading plus or minus, if not found, assume plus.
(1) Get a digit string, if none found, error out.
(2) If there's a dot, get another digit string, if not found, assume .00000
    (2a) get a letter, if it's 'E' or 'e':
           (2a.a)  get a sign, if not foiund. assume plus.
           (2.a.b) get a digit string, if not found, error out.
    (2b) if something other than 'E' or 'e' or white chars, error out
0

Featured Post

Netscaler Common Configuration How To guides

If you use NetScaler you will want to see these guides. The NetScaler How To Guides show administrators how to get NetScaler up and configured by providing instructions for common scenarios and some not so common ones.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

An Outlet in Cocoa is a persistent reference to a GUI control; it connects a property (a variable) to a control.  For example, it is common to create an Outlet for the text field GUI control and change the text that appears in this field via that Ou…
This tutorial is posted by Aaron Wojnowski, administrator at SDKExpert.net.  To view more iPhone tutorials, visit www.sdkexpert.net. This is a very simple tutorial on finding the user's current location easily. In this tutorial, you will learn ho…
The goal of this video is to provide viewers with basic examples to understand and use pointers in the C programming language.
The goal of this video is to provide viewers with basic examples to understand opening and reading files in the C programming language.

828 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question