برنامه ای که مفسر کامل بیسیک را پیاده سازی میکند
کتاب آموزش برنامه نویسی به زبان سی،مهندس عین ا.. جعفر نژاد قمی
#include <stdlib.h>
#include <conio.h>
#include <setjmp.h>
#include <math.h>
#include <ctype.h>
#include <stdio.h>
#include <string.h>
#define NUM_LAB 100
#define LAB_LEN 10
#define FOR_NEST 25
#define SUB_NEST 25
#define PROG_SIZE 10000
#define DELIMITER 1
#define VARIABLE 2
#define NUMBER 3
#define COMMAND 4
#define STRING 5
#define QUOTE 6
#define PRINT 1
#define INPUT 2
#define IF 3
#define THEN 4
#define FOR 5
#define NEXT 6
#define TO 7
#define GOTO 8
#define EOL 9
#define FINISHED 10
#define GOSUB 11
#define RETURN 12
#define END 13
int load_program(char *p ,char *fname);
char get_token();
void assignment();
int get_next_label(char *s);
int iswhite(char c);
int isdelim(char c);
char look_up(char *s);
int find_var(char *s);
char *gpop();
char *find_label(char *s);
struct for_stack fpop() ;
void print() , scan_labels() , find_eol(),exec_goto() ;
void exec_if() , exec_for(), next() ,fpush(struct for_stack i) ,input() ;
void gosub() , greturn() , gpush(char *s) , label_init() ;
void putback() , serror(int) , get_exp(int *) , primitive(int *result) ;
void level2(int *), level3(int *), level4(int *), level5(int *), level6(int *);
void arith(char o , int *r , int *h) , unary(char o , int *r) ;
char *prog ;
jmp_buf e_buf ;
int variable[26] = {0} ;
struct commands {
char commands[20] ;
char tok ;
} table[] = {
"print", PRINT, "input", INPUT, "if",IF,
"then", THEN, "goto", GOTO, "for", FOR ,
"next", NEXT , "to", TO , "gosub", GOSUB ,
"return", RETURN , "end", END , "", END } ;
char token[80], token_type, tok ;
struct label {
char name[LAB_LEN] ;
char *p ;
} ;
struct label label_table[NUM_LAB] ;
struct for_stack {
int var ;
int target ;
char * loc ;
} fstack[FOR_NEST] ;
char *gstack[SUB_NEST] ;
int ftos, gtos ;
int main(int argc, char *argv[])
{
char in[80] ;
int answer ;
char *p_buf , *t ;
clrscr();
if(argc != 2)
{
printf("\n usage : run < filename > ") ;
getch() ;
exit(1) ;
}
p_buf = (char *) malloc(PROG_SIZE) ;
if(!p_buf)
{
printf("\n allocation failure ") ;
getch() ;
exit(1) ;
}
if(!load_program(p_buf, argv[1]))
{
printf("\n file not loaded ") ;
getch() ;
exit(1) ;
}
if(setjmp(e_buf))
exit(1) ;
prog = p_buf ;
scan_labels() ;
ftos = 0 ;
gtos = 0 ;
do {
token_type = get_token() ;
if(token_type == VARIABLE) {
putback() ;
assignment() ;
}
else
switch(tok) {
case PRINT :
print() ; break ;
case GOTO :
exec_goto() ; break ;
case IF :
exec_if() ; break ;
case FOR :
exec_for() ; break ;
case NEXT :
next() ; break ;
case INPUT :
input() ; break ;
case GOSUB :
gosub() ; break ;
case RETURN :
greturn() ; break ;
case END :
exit(0) ;
}
} while (tok != FINISHED) ;
free(p_buf) ;
return 0;
}
//************
int load_program(char *p , char *fname)
{
FILE *fp ;
int i = 0 ;
fp = fopen(fname, "rb") ;
if(!fp)
return 0 ;
i = 0 ;
do {
*p = getc(fp) ;
p++ ; i++ ;
} while(!feof(fp) && i < PROG_SIZE) ;
*(p - 2) = '\0' ;
fclose(fp) ;
return 1 ;
}
//****************
void assignment()
{
int var , value ;
get_token() ;
if(!isalpha(*token)) {
serror(4) ;
return ;
}
var = toupper(*token) - 'A';
get_token() ;
if(*token != '=') {
serror(3) ;
return ;
}
get_exp(&value) ;
variable[var]=value ;
}
//****************
void print()
{
int answer , len=0 , spaces ;
char last_delim ;
do {
get_token() ;
if(tok == EOL || tok == FINISHED)
break ;
if(token_type == QUOTE) {
printf(token) ;
len += strlen(token) ;
get_token() ;
}
else {
putback() ;
get_exp(&answer) ;
get_token() ;
len += printf("%d",answer) ;
}
last_delim=*token ;
if(*token == ';') {
spaces = 8 - (len % 8) ;
len += spaces ;
while(spaces) {
printf(" ") ;
spaces -- ;
}
}
else if(*token == ',') ;//do nothing
else if(tok != EOL && tok != FINISHED)
serror(0) ;
} while(*token == ';' || *token == ',') ;
if(tok == EOL || tok == FINISHED) {
if(last_delim != ';' && last_delim !=',')
printf("\n") ;
}
else serror(0) ;
}
//*************************
void scan_labels()
{
int addr ;
char *temp ;
label_init() ;
temp = prog ;
get_token() ;
if(token_type == NUMBER) {
strcpy(label_table[0].name, token) ;
label_table[0].p = prog ;
}
find_eol() ;
do {
get_token() ;
if(token_type == NUMBER) {
addr = get_next_label(token) ;
if(addr == -1 || addr == -2) {
(addr == -1) ? serror(5) : serror(6) ;
} //end of if
strcpy(label_table[addr].name , token) ;
label_table[addr].p = prog ;
}//end of if
if(tok !=EOL)
find_eol() ;
} while(tok != FINISHED) ;
prog = temp ;
}
//******************
void find_eol()
{
while(*prog != '\n' && *prog != '\0')
++prog ;
if(*prog)
prog ++ ;
}
//******************
int get_next_label(char *s)
{
register int t ;
for(t = 0 ; t < NUM_LAB ; t++) {
if(label_table[t].name[0] == 0)
return t ;
if(!strcmp(label_table[t].name,s))
return -2 ;
} //end of for
return -1 ;
}
//*********************
char *find_label(char *s)
{
register int t ;
for(t = 0 ; t < NUM_LAB ; t++)
if(!strcmp(label_table[t].name, s))
return label_table[t].p ;
return '\0' ;
}
//******************
void exec_goto()
{
char *loc ;
get_token() ;
loc = find_label(token) ;
if(loc == '\0')
serror(7) ;
else prog = loc ;
}
//*******************
void label_init()
{
register int t ;
for(t = 0 ; t < NUM_LAB ; t++)
label_table[t].name[0] = '\0' ;
}
//*********************
void exec_if()
{
int x , y , cond ;
char op ;
get_exp(&x) ;
get_token() ;
if(!strchr("=<>", *token)) {
serror(0) ;
return ;
}
op = *token ;
get_exp(&y) ;
cond = 0 ;
switch(op) {
case '<' :
if(x < y) cond=1 ;
break ;
case '>' :
if(x > y) cond=1 ;
break ;
case '=' :
if(x == y) cond=1 ;
break ;
}//end of switch
if(cond) {
get_token() ;
if(tok != THEN) {
serror(8) ;
return ;
}
}//end of if
else find_eol() ;
}
//********************
void exec_for()
{
struct for_stack i ;
int value ;
get_token() ;
if(!isalpha(*token)) {
serror(4) ;
return ;
}
i.var = toupper(*token) - 'A' ;
get_token() ;
if(*token != '=') {
serror(3) ;
return ;
}
get_exp(&value) ;
variable[i.var] = value ;
get_token() ;
if(tok != TO) serror(9) ;
get_exp(&i.target) ;
if(value >= variable[i.var]) {
i.loc = prog ;
fpush(i) ;
}
else
while(tok!=NEXT) get_token() ;
}
//***************************
void next()
{
struct for_stack i ;
i = fpop() ;
variable[i.var]++ ;
if(variable[i.var] > i.target) return ;
fpush(i);
prog = i.loc ;
}
//***********************
void fpush(struct for_stack i)
{
if(ftos > FOR_NEST)
serror(10) ;
fstack[ftos] = i ;
ftos++ ;
}
//*********************
struct for_stack fpop()
{
ftos -- ;
if(ftos < 0) serror(11);
return(fstack[ftos]);
}
//***********************
void input()
{
char str[80], var ;
int i , ch , digit = 0 ;
get_token() ;
if(token_type == QUOTE) {
printf(token) ;
get_token() ;
if(*token != ',') {
serror(1) ;
}
get_token() ;
}
else printf("?") ;
var = toupper(*token) - 'A' ;
while(1) {
ch = getche() ;
if(ch <= 57 && ch >= 48) {
ch = ch - 48 ;
digit = (digit * 10) + ch ;
}
else if(ch == 13)
break ;
else {
printf("\Redo from start ?\n") ;
continue ;
}
}//end of while
variable[var]=digit ;
}
//**************
void gosub()
{
char *loc ;
get_token() ;
loc = find_label(token) ;
if(loc == '\0')
serror(7) ;
else {
gpush(prog) ;
prog = loc ;
}//end of else
}
//********************
void greturn()
{
prog = gpop() ;
}
//**************
void gpush(char *s)
{
gtos++ ;
if(gtos == SUB_NEST) {
serror(12) ;
return ;
}
gstack[gtos] = s ;
}
//*******************
char *gpop()
{
if(gtos == 0) {
serror(13) ;
return 0 ;
} //end of return
return(gstack[gtos --]) ;
}
//*****************
void putback()
{
char *t ;
t = token ;
for(; *t ; t++)
prog -- ;
}
//*****************
void serror(int error)
{
static char *e[] = {
"syntax error ",
"un balanced parantheses",
"no expressoin present" ,
"equals sign expexted" ,
"not a variable" ,
"label table full" ,
"dulicate label" ,
"undifined label" ,
"THEN expected" ,
"TO expected" ,
"too many nested FOR loops" ,
"NEXT without FOR" ,
"too many nested GOSUB",
"RETURN without GOSUB" } ;
printf("\n %s \n", e[error]) ;
longjmp(e_buf , 1) ;
}
//*****************
char get_token()
{
register char *temp ;
token_type = 0 ;
tok = 0 ;
temp = token ;
if(*prog == '\0') {
*token = 0 ;
tok = FINISHED ;
return(token_type = DELIMITER) ;
}//end of if
while(iswhite(*prog))
++ prog ;
if(*prog == '\r') {
++ prog ;
++ prog ;
tok = EOL ;
*token = '\r' ;
token[1] = '\n' ;
token[2] = 0 ;
return(token_type = DELIMITER) ;
}
if(strchr("+-*^/%=;(),><" , *prog)) {
*temp=*prog ;
prog ++ ;
temp ++ ;
*temp = 0 ;
return(token_type = DELIMITER) ;
}
if(*prog == '"') {
prog ++ ;
while(*prog != '"' && *prog != '\r')
*temp ++ = *prog ++ ;
if(*prog == '\r')
serror(1) ;
prog ++ ;
*temp = 0 ;
return(token_type = QUOTE) ;
} //end of if
if(isdigit(*prog)) {
while(!isdelim(*prog))
*temp ++= *prog ++ ;
*temp='\0' ;
return(token_type=NUMBER) ;
}
if(isalpha(*prog)) {
while(!isdelim(*prog))
*temp ++= *prog ++ ;
token_type = STRING ;
}
*temp='\0' ;
if(token_type == STRING) {
tok = look_up(token) ;
if(!tok)
token_type = VARIABLE ;
else
token_type = COMMAND ;
}
return token_type ;
}
//******************
char look_up(char *s)
{
register int i , j ;
char *p ;
p = s ;
while(*p) {
*p = tolower(*p) ;
p ++ ;
}
for( i= 0 ; *table[i].commands ; i++)
if(!strcmp(table[i].commands , s))
return table[i].tok ;
return 0 ;
}
//************
int isdelim(char c)
{
if(strchr(" ;,+-<>/*%^=()",c) || c == 9 ||
c=='\r' || c==0)
return 1 ;
return 0 ;
}
//**************
int iswhite(char c)
{
if(c == ' ' || c == '\t')
return 1 ;
else
return 0 ;
}
//***********************
void get_exp(int *result)
{
get_token() ;
if(!*token) {
serror(2) ;
return ;
}
level2(result) ;
putback() ;
}
//**********************
void level2(int *result)
{
register char op ;
int hold ;
level3(result) ;
while((op = *token) == '+' || op == '-') {
get_token() ;
level3(&hold) ;
arith(op , result , &hold) ;
}//end of while
}
//***************************
void level3(int * result)
{
register char op ;
int hold ;
level4(result) ;
while((op = *token) == '*' || op == '/' || op == '%')
{
get_token() ;
level4(&hold) ;
arith(op , result , &hold) ;
} //end of while
}
//******************
void level4(int * result)
{
int hold ;
level5(result) ;
if(*token == '^') {
get_token() ;
level4(&hold) ;
arith('^' , result , &hold) ;
}
}
//********************
void level5(int *result)
{
register char op ;
op = 0 ;
if((token_type == DELIMITER) && *token == '+' || *token == '-')
{
op = *token ;
get_token() ;
}
level6(result) ;
if(op)
unary(op , result) ;
}
//*******************************
void level6(int *result)
{
if((*token == '(') &&(token_type == DELIMITER))
{
get_token() ;
level2(result) ;
if(*token != ')')
serror(1) ;
get_token() ;
}
else
primitive(result) ;
}
//***********************
void primitive(int *result)
{
switch(token_type) {
case VARIABLE :
*result = find_var(token) ;
get_token() ;
return ;
case NUMBER :
*result = atoi(token) ;
get_token() ;
return ;
default :
serror(0) ;
}//end of switch
}
//*********************
void arith(char o , int *r , int *h)
{
register int t , ex ;
switch(o) {
case '-' :
*r = *r - *h ;
break ;
case '+' :
*r=*r + *h ;
break ;
case '*' :
*r=*r * *h ;
break ;
case '/' :
*r=(*r) / (*h) ;
break ;
case '%' :
t = (*r) / (*h) ;
*r = *r - (t * (*h)) ;
break ;
case '^' :
ex = *r ;
if(*h == 0) {
*r = 1 ;
break ;
}
for(t = *h - 1 ; t > 0 ; -- t)
*r=(*r) * ex ;
break ;
}//end of switch
}
//*************************
void unary(char o , int *r)
{
if(o == '-')
*r = -(*r) ;
}
//***************
int find_var(char *s)
{
if(!isalpha(*s)) {
serror(4) ;
return 0 ;
}
return variable[toupper(*token)-'A'] ;
}
//**********************
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