void main(void)
{
double opn1, opn2; /* working operands */
char s[LINE_SIZE]; /* input line buffer */
char opr; /* working operator */
char *p; /* buffer cursor */
printf("\nPrefix Form Evaluator");
printf("\n=====================");
printf("\n\nInput --> ");
gets(s);
initial(); /* initial stack */
for (p = s; *p != '\0'; p++) /* for each character */
if (is_opr(*p)) /* is is an operator ? */
push_opr(*p); /* YES, push. */
else if (isdigit(*p)) { /* is it an operand ? */
opn2 = *p - '0'; /* YES, convert to double */
while (stack_top() == OPERAND) {
opn1 = pop_opn(); /* for all of its */
opr = pop_opr(); /* buddy, compute */
opn2 = compute(opr, opn1, opn2);
}
push_opn(opn2); /* then push the result */
}
printf("\nResult = %lf", pop_opn());
}
leaf *build(char *expr, hashtab *h)
{
lstack s;
char opr;
int i = -1, num;
char str[MAX_STR];
leaf *l = NULL, *r = NULL, *tmp = NULL;
lstack_init(&s, 1024);
while (expr[++i])
{
if (is_digit(expr[i]))
{
num = get_number(expr, &i);
l = new_num_leaf(num, INT, NULL, NULL, -1);
lpush(&s, l);
}
else
if (is_opr(expr[i]))
{
lpop(&s, &r);
lpop(&s, &l);
//Optimization : reducing the amount of registers !!
if ((expr[i] == '+' || expr[i] == '*') && l->typ == INT && r->typ != INT)
tmp = l, l = r, r = tmp;
l = new_num_leaf(expr[i], CHAR, l, r, get_reg_num(l, r));
lpush(&s, l);
}
else
if (is_alpha(expr[i]))
{
get_string(expr, str, &i);
if (search(h, str))
{
lpop(&s, &r);
r->reg = 1; //Premice to register allocation !!!
l = new_str_leaf(str, FUNC, NULL, r, 1);
lpush(&s, l);
}
else //If not a function then a variable identifier ! [extend the grammar]
{
l = new_str_leaf(str, VAR, NULL, NULL, -1);
lpush(&s, l);
}
}
}
lstack_free(&s);
return l;
}
