C++ Programming Code Examples
C++ > Algorithms Code Examples
Regular exp to nfa
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/* 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();
}
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