checking syntax of a program ... starting and ending....

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1.00/5 (1 vote)

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i am working on parser phase of compiler for my assignment....
i am checking if the program has strated and ended correctly or not... when i read a file containing the correct syntax it display the message program starting missing.....
can anyone please help me... i will be very thankful...
here is my code......

C#

public bool pgStrtEnd(string str)
       {
           bool p = true;
           if (str.Contains("empty [") && str.Contains("]"))
        // if (str[0].Equals("empty [") && str[str.Length-1].Equals("]"))
           {
              // MessageBox.Show("Valid Program Start and End");
               p = true;
               return p;
           }
          // else // program starting and ending
         //  {
         //  else if (str[str.Length-1].Equals("]"))
           else  if (!str.Contains("]")) //str.Contains("empty [") &&
               {
                   MessageBox.Show("Program Ending Missing");
                   p =false;
                   return p;
               }
          // else if (str[0].Equals("empty [") )
           else if (!str.Contains("empty [")) // && str.Contains("]"))
               {
                   MessageBox.Show("Program Starting Missing");
                   p = false;
                   return p;
               }
           //else if (str.Contains("empty [") && str.Contains("]") && str.Any(char.IsLetterOrDigit))
           //{
           //    MessageBox.Show("Program has some extra after ending");
           //    p = true;
           //    return p;
           //}
               // return p;

           else
           {
               p = false;
               return p;
           }
          // }
        //   return p;
       }

Posted 12-May-14 10:32am

Member 10740412

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Comments

ZurdoDev 12-May-14 18:10pm

What is your question?

BillWoodruff 12-May-14 19:40pm

When are you going to learn to set break-points in your code, then single-step until you find an error, and determine exactly when errors, or unexpected results, occur ? If you take the trouble to learn/do this ... it's not that difficult ... you can start to post questions here that we can help you with.

3 solutions

Solution 2

To test whether a string start with given string and end with another string you could use String.StartsWith Method [^] and String.EndsWith Method[^]
before you call one of above method, you better trim the input string. (spaces at the start and end still valid)

C#

if(str.Trim().StartsWith("[")
{
   // your program start with "["
}

if(str.Trim().StartsWith("]")
{
   // your program start with "]"
}

I'm not going to comment on your parser because SA[^] already gave comprehensive answer.

Posted 12-May-14 17:12pm

DamithSL

Updated 12-May-14 17:13pm

v2

Solution 3

_After_ you learned about parser I suggest you to study a very straight Forward implementation: A Calculation Engine for .NET[^]

Posted 14-May-14 8:21am

idle63

Comments

Maciej Los 24-May-14 14:01pm

Good advice, Bruno!
+5!

[no name] 24-May-14 15:33pm

Thank you Maciej, Regards, Bruno

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Sergey Alexandrovich Kryukov · Accepted Answer · 2014-05-12T10:45:00

From the very beginning: this "parser" is wrong; so I don't want even to get into the detail of your problem.

You are not even close to starting a parser project yet. This is not how parsers work: they should be totally abstracted from any UI. You could collect all the problems in some data collection until it makes sense to continue parsing. You can even stop on the first unrecoverable problem if the input code and stop. But look what you are doing: showing MessageBox of every problem. Just imagine yourself to be a user of such "parser". More importantly, the bigger system hosting your parser, most likely, won't be even aware of the concept of MessageBox or any UI elements at all.

Also, you approach to a parse is totally ad-hoc, not using any regular approach. I can imagine someone doing a parser from scratch (because I did so, as well as many other people), but you don't have sufficient understanding yet, so your attempt already leads you nowhere. For example, you could formalize the notion of BNF syntax definition in your code and translate BNF into the parsing code. Instead, you need to read about the design of parsers (there are different well-known types of them) from some book on parsers. If this is your school assignment, could it be safe to assume that you had some lectures, seminars or learning courses covering this topic? :-)

Also, you could use on of available compier-compilers, but I'm not sure if it can be compatible with your assignment: http://en.wikipedia.org/wiki/Compiler-compiler[^].

See also:
http://en.wikipedia.org/wiki/Parsing[^],
http://en.wikipedia.org/wiki/Comparison_of_parser_generators[^].

—SA