关于Basic程序解释器及编译原理的简单化(1)---Basic器的语法分析及主要代码

关于Basic程序解释器及编译原理的简单化(1)---Basic器的语法分析及主要代码(2)     "goto",GOTO,
    "for",FOR,
    "next",NEXT,
    "to",TO,
    "gosub",GOSUB,
    "return",RETURN,
    "end",END,
    NULL,END
};

char token[80];
char token_type,tok;

struct label {
    char name [LAB_LEN];
    char *p;    /* point to place to go in source */
};

struct label label_table[NUM_LAB];
char *find_label(),*gpop();

struct for_stack {
    int var;   /* counter variable  */
    int target;  /* target value  */
    char *loc;
} fstack[FOR_NEST];  /* stack for FOR/NEXT loop  */
struct for_stack fpop();

char *gstack[SUB_NEST];  /* stack for gosub  */
int ftos;  /* index to top of FOR stack  */
int gtos;  /* index to top of GOSUB  */

void print(),scan_labels(),find_eol(),exec_goto();
void gosub(),greturn(),gpush(),label_init(),fpush();

/* Load a program */
load_program (char *p,char *fname)
{
    FILE *fp;
    int i=0;
   
    if (!(fp=fopen(fname,"rb")))  return 0;

    i=0;
    do  {
        *p = getc(fp);
        p++;i++;
    } while (!feof(fp)&&i<PROG_SIZE);
    *(p-2) = '\0';   /* null terminate the program  */
    fclose (fp);
    return 1;
}

/* assign a variable a value */
assignment()
{
    int var,value;

    /* getthe variable name */
    get_token();
    if (!isalpha(*token))  {
        serror(4);