Forth.c

#include <stdio.h>
#include <stdlib.h> /* for atof() */
#include <ctype.h>
#include <math.h>

#define MAXOP 100 /* max size of operator or operand */
#define MAXVAL 100 /* maximum depth of val stack */
#define NUMBER '0' /* signal that a number was found */
#define BUFSIZE 100
#define COMMAND 'A' /* signal that a command was found */

int getop(char []);
void push(double f);
double pop(void);
int getch(void);
void ungetch(int);

int sp = 0;
double val[MAXVAL];
char buf[BUFSIZE]; /* buffer for ungetch */
int bufp = 0; /* next free position in buf */

/* push: push f onto value stack */
void push(double f)
{
    if (sp < MAXVAL)
        val[sp++] = f;
    else
        printf("error: stack full, can't push %g\n", f);
}

/* pop: pop and return top value from stack */
double pop(void)
{
    if (sp > 0)
        return val[--sp];
    else {
        printf("error: stack empty\n");
        return 0.0;
    }
}

/* getop: get next character or numeric operand */
int getop(char s[])
{
    int i, c;

    while ((s[0] = c = getch()) == ' ' || c == '\t')
        ;
    s[1] = '\0';
    if (isalpha(c)) {
        while (isalpha(s[++i] = c = getch()))
            ;
        s[i] = '\0';
        printf("Entered string: %s\n", s);
        return COMMAND;
    }
    if (!isdigit(c) && c != '.' && c != '-')
        return c; /* not a number */
    i = 0;
    if (c == '-') { /* check to see if we have a neg number or a minus operator */
        s[++i] = c = getch();
        if (!isdigit(c)) /* if the next char is a number it's a neg num, else not */
            return '-';
    }
    if (isdigit(c)) { /* collect integer part */
        while (isdigit(s[++i] = c = getch()))
            ;
    }
    if (c == '.') /* collect fraction part */
        while (isdigit(s[++i] = c = getch()))
            ;
    s[i] = '\0';
    if (c != EOF)
        ungetch(c);
    return NUMBER;
}

int getch(void) /* get a (possibly pushed-back) character */
{
    return (bufp > 0) ? buf[--bufp] : getchar();
}

void ungetch(int c) /* push character back on input */
{
    if (bufp >= BUFSIZE)
        printf("ungetch: too many characters\n");
    else
        buf[bufp++] = c;
}

/* reverse Polish calculator */
main()
{
    int type, temp, i, sp_mark;
    double op2;
    char s[MAXOP];

    while ((type = getop(s)) != EOF) {
            switch (type) {
            case NUMBER:
                push(atof(s));
                break;
            case COMMAND:
                printf("s is: %s\n", s);
                if (s == "sin") {
                    printf("sin command received\n");
                    push(sin(pop()));
                    printf("\t%.8g\n", val[sp-1]);
                }
                break;
            case '+':
                push(pop() + pop());
                printf("\t%.8g\n", val[sp-1]);
                break;
            case '*':
                push(pop() * pop());
                printf("\t%.8g\n", val[sp-1]);
                break;
            case '-':
                op2 = pop();
                push(pop() - op2);
                printf("\t%.8g\n", val[sp-1]);
                break;
            case '/':
                op2 = pop();
                if (op2 != 0.0) {
                    push(pop() / op2);
                    printf("\t%.8g\n", val[sp-1]);
                }
                else
                    printf("error: zero divisor\n");
                break;
            case '%':
                op2 = pop();
                if (op2 != 0.0) {
                    push(fmod(pop(), op2));
                    printf("\t%.8g\n", val[sp-1]);
                }
                else
                    printf("error: zero divisor\n");
                break;
        /* ignore the rest of the cases, they're left over from previous exercise */
            case 'c': /* clears the stack */
                sp = 0;
                printf("All values cleared\n");
                break;
            case 's': /* shows the top values on the stack */
                if (sp > 1)
                    printf("The top elements on the stack are %.8g and %.8g\n",
                        val[sp-1], val[sp-2]);
                else if (sp == 1)
                    printf("The only element on the stack is %.8g\n", val[sp-1]);
                else
                    printf("The stack is empty\n");
                break;
            case 'S': /* swaps the top two elements */
                if (sp > 1) {
                temp = val[sp-1];
                val[sp-1] = val[sp-2];
                val[sp-2] = temp;
                }
                else
                    printf("Error: Not enough elements on stack\n");
                break;
            case 'd': /* duplicates the stack */
                if (sp > 0 && sp * 2 < MAXVAL - 1) {
                    for (i = 0, sp_mark = sp; i < sp_mark; i++)
                        push(val[i]);
                }
                else if (sp == 0)
                    printf("Error: Stack is empty");
                else
                    printf("Error: Insufficient space on stack");
                break;
            case '\n':
                /* printf("\t%.8g\n", pop()); */
                printf("\n");
                break;
            default:
                printf("error: unknown command %s\n", s);
                break;
            }
    }
    return 0;
}