Turing Machine Implementation in C
I'm studying Turing machines for my course in formal languages theory, the professor recommended a run on the following algorithm to see in detail the logic behind of a "TM", but doesn't work, when trying to compile tells me the following error.
C:\Documents and Settings\Melkhiah.EQUIPO01\Mis documentos\Downloads\Tarea3 Discretas\TM.c||In function `Tape* insert_tape(Tape*, Direction, char)':|
C:\Documents and Settings\Melkhiah.EQUIPO01\Mis documentos\Downloads\Tarea3 Discretas\TM.c|44|error: invalid conversion from `void*' to `Tape*'|
C:\Documents and Settings\Melkhiah.EQUIPO01\Mis documentos\Downloads\Tarea3 Discretas\TM.c||In function `Tape* create_tape(char*)':|
C:\Documents and Settings\Melkhiah.EQUIPO01\Mis documentos\Downloads\Tarea3 Discretas\TM.c|68|error: invalid conversion from `void*' to `Tape*'|
C:\Documents and Settings\Melkhiah.EQUIPO01\Mis documentos\Downloads\Tarea3 Discretas\TM.c||In function `Transition* get_transition(char*)':|
C:\Documents and Settings\Melkhiah.EQUIPO01\Mis documentos\Downloads\Tarea3 Discretas\TM.c|80|error: invalid conversion from `void*' to `Transition*'|
C:\Documents and Settings\Melkhiah.EQUIPO01\Mis documentos\Downloads\Tarea3 Discretas\TM.c||In function `List* insert_list(List*, char*)':|
C:\Documents and Settings\Melkhiah.EQUIPO01\Mis documentos\Downloads\Tarea3 Discretas\TM.c|93|error: invalid conversion from `void*' to `List*'|
C:\Documents and Settings\Melkhiah.EQUIPO01\Mis documentos\Downloads\Tarea3 Discretas\TM.c||In function `List* insert_list_transition(List*, Transition*)':|
C:\Documents and Settings\Melkhiah.EQUIPO01\Mis documentos\Downloads\Tarea3 Discretas\TM.c|105|error: invalid conversion from `void*' to `List*'|
C:\Documents and Settings\Melkhiah.EQUIPO01\Mis documentos\Downloads\Tarea3 Discretas\TM.c||In function `TM* createTM(char*)':|
C:\Documents and Settings\Melkhiah.EQUIPO01\Mis documentos\Downloads\Tarea3 Discretas\TM.c|166|error: invalid conversion from `void*' to `TM*'|
C:\Documents and Settings\Melkhiah.EQUIPO01\Mis documentos\Downloads\Tarea3 Discretas\TM.c|167|error: invalid conversion from `void*' to `List*'|
||=== Build finished: 7 errors, 0 warnings ===|
here's the code:
/* This C file implements a Non-determinitic Pushdown Automata
* author: Kevin Zhou
* Computer Science and Electronics
* University of Bristol
* Date: 21st April 2010
*/
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
typedef struct tapes {
struct tapes *left;
struct tapes *right;
char content;
} Tape;
typedef enum { LEFT,RIGHT } Direction;
typedef struct transition {
char current_state;
char tape_symbol;
char new_state;
char new_tape_symbol;
Direction dir;
} Transition;
typedef struct list {
Transition *content;
struct list *next;
} List;
typedef struct tm {
char *input_alpha;
char *input;
char *tape_alpha;
char start;
char accept;
char reject;
List *transition;
} TM;
Tape *insert_tape(Tape *t, Direction dir, char c) {
Tape *head = t;
Tape *new1 = calloc(1,sizeof(Tape));;
new1 -> content = c;
if(dir == LEFT) {
while(t->left != NULL) {
t = t->left;
}
new1->right = t;
new1->left = NULL;
t->left = new1;
return new1;
}
if(dir == RIGHT) {
while(t->right != NULL) {
t = t->right;
}
new1->left = t;
new1->right = NULL;
t->right = new1;
}
return head;
}
Tape *create_tape(char *input) {
int i=1;
Tape *t = calloc(1,sizeof(Tape));
t->content = input[0];
while(1) {
if(input[i] == '\0') break;
t = insert_tape(t,RIGHT,input[i]);
i++;
}
return t;
}
/* turn the input string into Transition fields */
Transition *get_transition(char *s) {
Transition *t = calloc(1,sizeof(Transition));
Direction dir;
t->current_state = s[0];
t->tape_symbol = s[1];
t->new_state = s[2];
t->new_tape_symbol = s[3];
dir = (s[4]=='R')? RIGHT:LEFT;
t->dir = dir;
return t;
}
/* turn the string into transitions and add into list */
List *insert_list( List *l, char *elem ) {
List *t = calloc(1,sizeof(List));
List *head = l;
while(l->next!=NULL)
l = l->next;
t->content = get_transition(elem);
t->next = NULL;
l->next = t;
return head;
}
/* insert a transition into a list */
List *insert_list_transition( List *l, Transition *tr) {
List *t = calloc(1,sizeof(List));
List *head = l;
while(l->next!=NULL)
l = l->next;
t->content = tr;
t->next = NULL;
l->next = t;
return head;
}
void print_tape( Tape *t,char blank) {
char c;
while(1) {
if(t->content != blank) break;
t= t->right;
}
while(1) {
if(t==NULL) break;
c = t->content;
if(t->content != blank)
putchar(c);
t= t->right;
}
putchar('\n');
}
void print_transition (Transition *t) {
char s1[] = "Left";
char s2[] = "Right";
if(t==NULL) {
printf("NULL Transfer");
return;
}
printf("current:%c tape:%c new state:%c new tape:%c direction %s\n",t->current_state,t->tape_symbol,t->new_state,t->new_tape_symbol,(t->dir == LEFT)?s1:s2);
}
/*test if the char c is in the string s */
int contains ( char c, char *s ) {
int i=0;
while(1) {
if(c== s[i]) return 1;
if(s[i] == '\0') return 0;
i++;
}
}
/* test if the input is a valid input */
int is_valid_input( char *input_alpha, char *input ) {
int i=0;
char c;
while(1) {
c = input[i];
if(c == '\0') break;
if(!contains(c,input_alpha)) return 0;
i++;
}
return 1;
}
TM *createTM (char *input) {
TM *m = calloc(1,sizeof(TM));
List *tr = calloc(1,sizeof(List));
char *buffer;
/*read input alphabet of PDA*/
buffer = strtok(input,":");
if(buffer == NULL) {
printf("Error in reading input alphabet!\n");
exit(1);
}
m->input_alpha = buffer;
/*read tape alphabet*/
buffer = strtok(NULL,":");
if(buffer == NULL) {
printf("Error in reading tape alphabet!\n");
exit(1);
}
m->tape_alpha = buffer;
/*read input sequence*/
buffer = strtok(NULL,":");
if(buffer == NULL) {
printf("Error in reading input sequence!\n");
exit(1);
}
if(!is_valid_input(m->input_alpha,buffer)) {
printf("Error! Input contains some invalid characters that don't match the input alphabet!\n");
exit(1);
}
m->input = buffer;
buffer = strtok(NULL,":");
m->start = buffer[0];
buffer = strtok(NULL,":");
m->accept = buffer[0];
buffer = strtok(NULL,":");
m->reject = buffer[0];
/*read tape transition*/
while(1) {
buffer = strtok(NULL,":");
if(buffer == NULL) break;
tr = insert_list(tr,buffer);
}
m->transition = tr->next;
return m;
}
Transition *find_transition(List * list,char state, char tape_symbol) {
Transition *t;
while(1) {
if(list==NULL) return NULL;
t = list -> content;
if(t->current_state == state && t->tape_symbol == tape_symbol)
return t;
list = list->next;
}
}
Tape *move(Tape *t,Direction dir, char blank) {
if(dir == LEFT) {
if(t->left==NULL) {
t = insert_tape(t,LEFT,blank);
}
return t->left;
}
if(dir == RIGHT) {
if(t->right==NULL) {
t = insert_tape(t,RIGHT,blank);
}
return t->right;
}
return NULL;
}
void simulate( TM *m ) {
/* first symbol in input symbol used to represent the blank symbol */
const char blank = m->tape_alpha[0];
char current_state = m->start;
Tape *tape = create_tape(m->input);
Tape *current_tape = tape;
char current_tape_symbol;
Transition *current_transition;
while(1) {
if(current_state == m->accept) {
printf("Accept\n");
print_tape(tape,blank);
break;
}
if(current_state == m->reject) {
printf("Reject\n");
print_tape(tape,blank);
break;
}
current_tape_symbol = (current_tape==NULL||current_tape ->content == '\0')?blank:current_tape->content;
current_transition = find_transition(m->transition,current_state,current_tape_symbol);
current_state = current_transition -> new_state;
current_tape -> content = current_transition -> new_tape_symbol;
current_tape = move( current_tape, current_transition ->dir, blank);
}
}
int main(void) {
char s[300];
TM *p;
scanf("%s",s);
p = createTM(s);
simulate(p);
return 0;
}
Why is this program not work?
Answer
The program provided is in C, however, you're compiling with a C++ compiler.
Compile again using C, and you should be ok.