code for displaying that the given number is not a real number if it contains two dots in C#

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code for displaying that the given number is not a real number if it contains two dots in C#.

i am working on lexical analyzer phase of complier construction. i hava written a code that display the number as a real number if it contains one dot int it, but if it contains two dot it does not generate an error.
here is my code..........

C#

bool containReal = ss.Any(char.IsDigit) && ss.Contains('.');
                                       if (containReal)
                                       {
                                           MessageBox.Show("this is a Real Number");
                                           break;
                                       }
                                       //invalid b/c of two dots
                                       string str2 = ss.Substring(1, ss.IndexOf('.'));
                                       string str3 = ss.Substring(ss.IndexOf('.') + 1);
                                       bool chk_dot = (str2.Any(char.IsLetter) || str3.Any(char.IsLetter) || str2.IndexOfAny("!@%^&*()#$-_+<>".ToCharArray()) != -1 || str3.IndexOfAny("!@%^&*()#$-_+<>".ToCharArray()) != -1);
 if ( chk_dot)
                                        {
                                            MessageBox.Show("Error: Line num  " + linecount + "  Invalid b/c of two dots in a real number");
                                            errorcount++;
                                            break;

                                        }

can anyone please help me................

Posted 11-Apr-14 14:48pm

Member 10740412

Updated 11-Apr-14 15:24pm

v4

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Comments

PIEBALDconsult 11-Apr-14 21:02pm

Perhaps a Regular Expression? http://www.regular-expressions.info/floatingpoint.html

Judging by your code, you should not be writing a compiler.

Member 10740412 11-Apr-14 21:32pm

just doing assignmet. not building a real compiler...

[no name] 11-Apr-14 21:21pm

What happened to the answers you already have? And, I would really like to answer but since you cross-posted I am confused which place I would answer.

Member 10740412 11-Apr-14 21:28pm

the latest post

[no name] 11-Apr-14 21:37pm

But which one is that? Did you even bother running this code through a debugger? The answer is obvious if you did. What is it that you think is going to happen at the very first line of code if you have a string like "123.45.67"? ss.Contains('.') is true right? So you popup a message box and exit whatever loop you are in. Don't you think that you should be checking if 'ss' contains two dots before you break out?

Member 10740412 11-Apr-14 21:40pm

it diplays that the number is real number either it has one or two dots.

[no name] 11-Apr-14 21:41pm

Yes. Because that is what you told it to do!

[no name] 11-Apr-14 21:42pm

It's going to say that whether ss contains 1 or 50 dots.

Member 10740412 11-Apr-14 21:47pm

then can you tell me how to do it....

[no name] 11-Apr-14 21:53pm

Try commenting out the whole block of :
if (containReal)
{
MessageBox.Show("this is a Real Number");
break;
}
And rethink how you are really trying to do this. IF you really need to inform the user that the number is "real" then do something like "
if ( chk_dot)
{
show your error
{
else
{
show real message
}

Member 10740412 11-Apr-14 21:56pm

okay going to try it

PIEBALDconsult 11-Apr-14 21:59pm

I strongly advise against using Substring.

[no name] 11-Apr-14 22:02pm

Agreed. Completely unnecessary.

Sergey Alexandrovich Kryukov 11-Apr-14 22:01pm

I think the whole idea to analyze the content of the literal makes no sense. Please see my answer.
—SA

[no name] 11-Apr-14 22:02pm

He is just learning.

Sergey Alexandrovich Kryukov 11-Apr-14 22:05pm

I understand, but "learning" should not mean doing useless work. There are way too many tasks we could offer to the beginner, more related to reality. There are many other tasks to learn string manipulations and, say, regular expressions. Lexical analyzers themselves are difficult enough to write, so there is no need in doing unnecessary work. Can you see my point?
—SA

[no name] 11-Apr-14 22:28pm

Oh yes I see your point but hitting a beginner with a lot of technical jargon that does not make any sense to them does not do any good either. We have no idea where "ss" is even coming from so passing judgement on his technique does no do any good at all.

Sergey Alexandrovich Kryukov 11-Apr-14 22:45pm

True, but I don't understand what do you mean by this jargon and other 'hitting' things...
I suggested much easier and practical approach, that's all that matters.
—SA

[no name] 11-Apr-14 22:00pm

Forget that. try:
int first = ss.IndexOf('.');
int next = ss.IndexOf('.', first + 1);
bool chk_dot = first > 0 && next > 0;
if (chk_dot)
{
MessageBox.Show("Error: Line num Invalid b/c of two dots in a real number");
//errorcount++;
break;

}
else
{
MessageBox.Show("Real");

}

Member 10740412 11-Apr-14 22:17pm

thanx its working.....

[no name] 11-Apr-14 22:29pm

Good! Congrats. Learn to use the debugger and you will have a very valuable skill at your disposable.

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Sergey Alexandrovich Kryukov · Answer 1 · 2014-04-11T15:59:00

There are many questions on validation of real numbers using different artificial methods. You don't need any of them. Say, the number is declared as double. The the validation is:

C#

string numericLiteral = // from input of the analyzer, part of user's code
bool isValid = double.TryParse(numericLiteral, out value);

That's is. Nobody cares what's exactly wrong in the literal; compilers never show it in the error description. You can only show the value of the literal and tell the user if isValid == false: "invalid numeric format".

—SA