Thread: Building a NFA help

I am trying to create a NFA from a regular expression. I have a grasp on reading in the regular expression and being able to make a stack from it. The part I am struggling on is mapping the characters in the regular expression to an integer indicating the variables order in the expression. I am just not sure how to go about this. Any help is welcome. My code so far...

Code:

#include<stdio.h>
#include<stdlib.h>
#include "stack.h"


int main(void)
{
	char expression[80];//array to store regular expression
	char capital[130];//Array to store capital letters
	int i=0,x=0,y=0,z=65;
	char input;


	while(scanf("%c",&input) != EOF){//check for end of input
		if(!isspace((unsigned char)input)){//skip whitespaces
			if((input != ')')&&(input != '(')){
				for(i=i;i<80;i++){//initialize array with input
					expression[x]=input;
					x++;
					break;
				}
				for(y=y;y<91;y++){//initialize letter array
					if(input>=65 && input<=90){//check for capital
						capital[input]=input;
						pushChar(input);
					}
					break;
				}
			}
		}
	}




	for(z=z;z<91;z++){
		if(capital[z]>=65 && capital[z]<=90){//Print each letter once
			printf("%c ",capital[z]);
		}
	}
	printf("\n\n");


	for(i=0;i<x;i++)//printing full regular expression
		printf("%c",expression[i]);




	printf("\n");




	return 0;
}

Originally Posted by crashband

Code:

for(i=i;i<80;i++){//initialize array with input
    expression[x]=input;
    x++;
    break;
}
for(y=y;y<91;y++){//initialize letter array
    if(input>=65 && input<=90){//check for capital
        capital[input]=input;
        pushChar(input);
    }
    break;
}

What is the logic behind using for loop like this? I don't see any.

Originally Posted by DRK

What is the logic behind using for loop like this? I don't see any.

It is to put the full regular expression in one array and just the capital letters in another. It worked which I guess is the most important thing. How would you have put it?

Originally Posted by crashband

It is to put the full regular expression in one array and just the capital letters in another. It worked which I guess is the most important thing. How would you have put it?

Probably with strcpy and isupper. (Admittedly I don't really know why we care about capitals, but I'm assuming you know so I guess that's okay.)

As to the question, I'm not sure I know what you mean by this mapping. Do you mean you want an array such that, if (say) the first parenthesized expression matched characters 18-21 in the array, then array[17] through array[20] would be 1? Or something else?

Originally Posted by tabstop

Probably with strcpy and isupper. (Admittedly I don't really know why we care about capitals, but I'm assuming you know so I guess that's okay.)

As to the question, I'm not sure I know what you mean by this mapping. Do you mean you want an array such that, if (say) the first parenthesized expression matched characters 18-21 in the array, then array[17] through array[20] would be 1? Or something else?

By mapping I mean mapping one of the letters to an integer and the integer will represent the column numbers in the state table. That is how my professor put it if that makes sense.

Originally Posted by crashband

By mapping I mean mapping one of the letters to an integer and the integer will represent the column numbers in the state table. That is how my professor put it if that makes sense.

Juuuust realized that we're talking about those kinds of regular expressions. Anyway.

First off: you should probably try to forget 65 and 90. You can use 'A' and 'B' and ... and 'Z' as numbers already (because they are). I'm assuming the capital letters are your input/alphabet? If so, I don't see a reason to keep a bunch of columns around that you're not going to use; I would suggest just creating 26 columns, and address them using 'A' - 'A', 'B' - 'A' , ..., 'Z' - 'A'.

Any luck with your code?