Initial commit

c++/Others/Regular exp to nfa.cpp

@@ -0,0 +1,76 @@
+Regular exp to nfa
+
+# include <stdio.h>
+# include <conio.h>
+# include <string.h>
+# include <ctype.h>
+// regular expression to nfa by g.ram kumar
+// works for everything but produces excessive epsilon transitions
+int ret[100];
+static int pos=0;
+static int sc=0;
+void nfa(int st,int p,char *s)
+{    int i,sp,fs[15],fsc=0;
+	sp=st;pos=p;sc=st;
+	while(*s!=NULL)
+	{if(isalpha(*s))
+	    {ret[pos++]=sp;
+		ret[pos++]=*s;
+		ret[pos++]=++sc;}
+	if(*s=='.')
+		{sp=sc;
+		 ret[pos++]=sc;
+		 ret[pos++]=238;
+		 ret[pos++]=++sc;
+		 sp=sc;}
+	if(*s=='|')
+		{sp=st;
+		 fs[fsc++]=sc;}
+	if(*s=='*')
+		{ret[pos++]=sc;
+		 ret[pos++]=238;
+		 ret[pos++]=sp;
+		 ret[pos++]=sp;
+		 ret[pos++]=238;
+		 ret[pos++]=sc;
+		 }
+	 if (*s=='(')
+		{char ps[50];
+		 int i=0,flag=1;
+		 s++;
+		   while(flag!=0)
+			{ps[i++]=*s;
+			 if (*s=='(')
+				flag++;
+			 if (*s==')')
+				flag--;
+			 s++;}
+			 ps[--i]='\0';
+			 nfa(sc,pos,ps);
+			 s--;
+		}
+	 s++;
+	}
+	sc++;
+	  for(i=0;i<fsc;i++)
+		 {ret[pos++]=fs[i];
+		  ret[pos++]=238;
+		  ret[pos++]=sc;
+		 }
+		  ret[pos++]=sc-1;
+		  ret[pos++]=238;
+		  ret[pos++]=sc;
+}
+void main()
+{    int i;
+	char *inp;
+	clrscr();
+	printf("enter the regular expression :");
+	gets(inp);
+	nfa(1,0,inp);
+	printf("\nstate  input  state\n");
+	for(i=0;i<pos;i=i+3)
+		 printf("%d     --%c-->      %d\n",ret[i],ret[i+1],ret[i+2]);
+	printf("\n");
+	getch();
+}