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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(6) } /* find location of given label. A null is returned if
label is not found; ohtherwise a pointer to the position
of the label is returned.
*/
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'; /* error condition */
}
/* execute a GOTO statement. */
void exec_goto()
{
char *loc;
get_token(); /* get label to go to */
/* find the location of label */
loc = find_label (token);
if (loc=='\0')
serror(7); /* label not defined */
else prog=loc; /* start program running at that time */
}
/* initialize the array that holds the labels.
by convention , a null label name indicates that
array posiiton is unused.
*/
void label_init()
{
register int t;
for (t=0;t<NUM_LAB;++t) label_table[t].name[0]='\0';
}
/* execute an IF statement */
void exec_if()
{
int x,y,cond;
char op;
get_exp(&x); /* get left exapression */ get_token(); /* get the operator */
if (!strcmp("<>",*token)) {
serror(0); /* not a leagal oprator */
return;
}
op = *token;
get_exp(&y); /* get right expression */ /* determine the outcome */
cond = 0;
switch(op) {
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