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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(8) get_exp(&value); /* get initial value */ variables[i.var]=value; get_token(); if (tok != TO) serror(9); /* read an discard the TO */
get_exp(&i.target); /* get target value */ /* if loop can execute at least once, push into on stack */
if (value<=i.target) {
i.loc = prog;
fpush(i);
}
else /* otherwise, skip loop code altogether */
while (tok!=NEXT) get_token();
}
/* execute a NEXT statement */
void next()
{
struct for_stack i;
i = fpop(); /*read the loop info */ variables[i.var]++; /* increment control variable */
if (variables[i.var]>i.target) return; /* all done */
fpush(i); /* otherwise,return the info */
prog = i.loc; /* loop */
}
/* push function for the FOR stack */
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]);
}
/* exec a simple form of BASIC INPUT command */
void input()
{
char str[80],var;
int i;
get_token(); /* see if prompt string id=s present */
if (token_type == QUOTE) {
printf (token); /* if so , print it and check for command */
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