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initial_divisor/main.c

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+#include <stdlib.h>
+#include <stdio.h>
+#include "turing.h"
+#include "states.h"
+#include "const.h"
+
+#define REJECT -1
+#define ACCEPT -2
+
+// gcc -g main.c turing.c states.c turing.h states.h const.h -o main
+
+int main(){
+
+	int List[] = {0,1,1,8,2,2,9};
+	int longitud=7;
+	int state=0;
+	int position=0;
+	int symbol= List[position];
+	int movement =0; // undefined.
+	int placeholder;	
+	
+
+	while(state!=ACCEPT && state!=REJECT){
+
+		print_lista(List, longitud, position);
+		print_variables(state,position,symbol, movement);		
+		fscanf(stdin,"\n%d", &placeholder);
+
+		carry_out_step(&symbol,&state,&movement);
+		
+		if(state!=ACCEPT && state!=REJECT){
+			List[position]=symbol;
+			position = position +movement;	
+			symbol=List[position];
+		}
+		
+	}
+
+	
+
+}

initial_divisor/states.c

@@ -0,0 +1,206 @@
+#include <stdlib.h>
+#include <stdio.h>
+#include "const.h"
+#include "states.h"
+
+// States of a Turing Machine that checks whether a number DOESN'T divide another number
+// NTS: Check that the first number is smaller? Actually not necessary: see state 2.
+
+/*
+Initially, I defined a triplet, which was what the different states, which are functions returned.
+
+typedef struct  {
+
+	int state; // Finite list of states: initial (0), state 1, state 2, state 3, ..., state 7.
+	int symbol; // Finite list of symbols: 0,1,2,3,4,5,6,7,8,9
+	int movement; // Left = -1, Right =1;
+
+}  ssm;
+
+But I thought that modifying pointers was easier and more elegant.
+*/
+
+void state0(int *symbol, int *state, int *movement);
+void state1(int *symbol, int *state, int *movement);
+void state2(int *symbol, int *state, int *movement);
+void state3(int *symbol, int *state, int *movement);
+void state4(int *symbol, int *state, int *movement);
+void state5(int *symbol, int *state, int *movement);
+void state6(int *symbol, int *state, int *movement);
+void state7(int *symbol, int *state, int *movement);
+
+// This function is the delta of which Kozen speaks of in p.210 &ss in Automata and Computability.
+void carry_out_step(int *symbol, int *state, int *movement){  // I could make this a bigger if/else tree, but I don't want to.
+// Initially, I thought to use https://stackoverflow.com/questions/840501/how-do-function-pointers-in-c-work, but this proved unnecessary.
+	
+	if(*state==0){
+		state0(symbol,state, movement);
+	}
+	else if(*state==1){ 
+	// Nótese que los else ifs son necesarios, porque después de state0, *state es =1, pero queremos que se de cuenta en la siguiente vuelta
+		state1(symbol,state, movement);
+	}
+	else if(*state==2){
+		state2(symbol,state, movement);
+	}
+	else if(*state==3){
+		state3(symbol,state, movement);
+	}
+	else if(*state==4){
+		state4(symbol,state, movement);
+	}
+	else if(*state==5){
+		state5(symbol,state, movement);
+	}
+	else if(*state==6){
+		state6(symbol,state, movement);
+	}	
+	else if(*state==7){
+		state7(symbol,state, movement);
+	}
+
+}
+
+void state0(int *symbol, int *state, int *movement){
+	if(*symbol ==0){
+		*symbol=0; // This is the left endmarker. It isn't changed. This line could be ommited.
+		*movement= 1; // Move to the right (0 would be to the left).
+		*state=1; // Change to state 1.
+	}
+
+	else{
+		fprintf(stdout,"\nEn state0, REJECT");
+		*state = REJECT; // This is defined as a constant in const.h 
+		// The program ends, because it has unspecified behaviour
+	}
+
+}
+
+void state1(int *symbol, int *state, int *movement){
+	if(*symbol ==1){
+		*symbol=3; // Another symbol.
+		*movement= 1; // Move to the right (-1 would be to the left).
+		*state=2; // Change to state 2.
+	}
+
+	else{
+		fprintf(stdout,"\nEn state1, REJECT");
+		*state = REJECT; // This is defined as a constant in const.h 
+		// The program ends, because it has unspecified behaviour
+	}
+}
+
+void state2(int *symbol, int *state, int *movement){
+
+	if(*symbol ==2){
+		*symbol=4; // You get the idea.
+		*movement= -1; 
+		*state=3; 
+	}
+
+	else if(*symbol ==9){
+		*state=ACCEPT; 
+		fprintf(stdout,"\nIt accepts because the first number doesn't divide the second");
+	}
+
+	else{
+		*symbol=*symbol; // redundant
+		*movement= 1; 
+		*state=2; 
+	}
+}
+
+void state3(int *symbol, int *state, int *movement){
+
+	if(*symbol ==0){
+		*symbol=0; 
+		*movement= 1; 
+		*state=4; 
+	}
+
+	else {
+		*symbol=*symbol;
+		*movement = -1;
+		*state= 3;
+	}
+}
+
+void state4(int *symbol, int *state, int *movement){
+
+	if(*symbol ==3){
+		*symbol=3; 
+		*movement= 1; 
+		*state=4; 
+	}
+
+	else if(*symbol ==1){
+		*symbol=1; 
+		*movement= -1; 
+		*state=5; 
+	}
+
+	else if(*symbol ==8){
+		*symbol=8; 
+		*movement= 1; 
+		*state=6; 
+	}
+
+	else{
+		*state = REJECT; // This is defined as a constant in const.h 
+		// The program ends, because it has unspecified behaviour
+	}
+}
+
+void state5(int *symbol, int *state, int *movement){ 
+// This state comes to be because at the end of option symbol ==1 in state 4, I want to stay on the same place, but have to move.
+	*symbol =*symbol;
+	*movement = 1;
+	*state = 1;
+}
+
+void state6(int *symbol, int *state, int *movement){
+
+	if(*symbol ==2){
+		*symbol=4; 
+		*movement=-1; 
+		*state=7; 
+	}
+
+	else if(*symbol ==9){
+		*symbol=9; 
+		*movement=-1; 
+		*state = REJECT; 
+		fprintf(stdout,"\nIt rejects because the first number DOES divide the second\n");// The number does divide.
+	}
+
+	else{
+		*symbol = *symbol;
+		*movement =1;
+		*state=6;
+	}
+
+}
+
+void state7(int *symbol, int *state, int *movement){
+
+	if(*symbol ==3){
+		*symbol=1; 
+		*movement=-1; 
+		*state=7; 
+	}
+
+	else if(*symbol ==0){
+		*symbol=0; 
+		*movement= 1; 
+		*state = 1; 
+	}
+
+	else{
+		*symbol = *symbol;
+		*movement =-1;
+		*state=7;
+	}
+
+}
+
+

initial_divisor/states.h

@@ -0,0 +1,6 @@
+#ifndef __STATES_H_
+#define __STATES_H_
+
+void carry_out_step(int *symbol, int *state, int *movement); // This is the only function I'm going to need to use outside of states.c
+
+#endif

initial_divisor/turing.c

@@ -0,0 +1,59 @@
+#include <stdlib.h>
+#include <stdio.h>
+#include "turing.h"
+#include "const.h"
+
+// Turing print defines functions that take a list, take a position in that list and print the list with a pointer to that position.
+// It prints this vertically
+
+void print_lista(int*L, int length, int position){
+	if(L==NULL || length <= position){
+		fprintf(stdout, "\nError en prettyprint");
+	}
+	else{
+		int i=0;
+		char tabs[]="\t\t\t\t\t\t";
+		for(i=0; i<length; i++){
+			if(i==position){
+				fprintf(stdout, "\n%s{",tabs);
+			}
+			else{
+				fprintf(stdout, "\n%s",tabs);
+			}
+
+			if( L[i]==0){
+					fprintf(stdout, "T");
+
+			}
+
+			else if(L[i]==8){
+					fprintf(stdout, "X");
+			}
+
+			else if(L[i]==9){
+					fprintf(stdout, "W");
+			}
+
+			else{
+					fprintf(stdout, "%d",L[i]);
+			}
+
+			if(i==position){
+				fprintf(stdout, "}\n");
+			}
+			else{
+				fprintf(stdout, "\n");
+			}
+		}
+
+	}
+
+}
+
+void print_variables(int state, int position, int symbol,  int movement){
+	fprintf(stdout,"\nState =%d\n",state);
+	fprintf(stdout,"\nPosition =%d\n",position);
+	fprintf(stdout,"\nSymbol =%d\n",symbol);
+	fprintf(stdout,"\nMovement =%d\n\n",movement);
+}
+

initial_divisor/turing.h

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+#ifndef __CONST_H_
+#define __CONST_H_
+
+void print_lista(int*L, int length, int position);
+void print_variables(int state, int position, int symbol,  int movement);
+#endif