Exercise 4.5 - RPN Calculator with mathematical functions¶

/* Include Mathematical Functions */
/* Add commands to
  - print top element of the stack,without poping
  - duplicate it
  - swap the top two elements
  - Clear the stack  */

/* IMPORTANT: compile with -lm flag(the static math library)
   For eg: gcc -lm rpn-3.c
*/

#include <ctype.h>
#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define MAXOP 100
#define NUMBER '0'
#define NAME 'n'
#define BUFSIZE 100
#define MAXVAL 100

int sp = 0;
double val[MAXVAL];
char buf[BUFSIZE];
int bufp = 0;

int getch(void);

void ungetch(int);

int getop(char[]);

void push(double);

double pop(void);

void mathfnc(char[]);

/* reverse polish calculator */

int main(void) {
    int type;
    double op2, op1;
    char s[MAXOP];
    void clearsp(void);

    while ((type = getop(s)) != EOF) {
        switch (type) {
            case NUMBER:
                push(atof(s));
                break;
            case NAME:
                mathfnc(s);
                break;
            case '+':
                push(pop() + pop());
                break;
            case '*':
                push(pop() * pop());
                break;
            case '-':
                op2 = pop();
                push(pop() - op2);
                break;
            case '/':
                op2 = pop();
                if (op2 != 0.0)
                    push(pop() / op2);
                else
                    printf("error:zero divisor\n");
                break;
            case '%':
                op2 = pop();
                if (op2 != 0.0)
                    push(fmod(pop(), op2));
                else
                    printf("erro:zero divisor\n");
                break;
            case '?':
                op2 = pop();
                printf("\t%.8g\n", op2);
                push(op2);
                break;
            case 'c':
                clearsp();
                break;
            case 'd':
                op2 = pop();
                push(op2);
                push(op2);
                break;
            case 's':
                op1 = pop();
                op2 = pop();
                push(op1);
                push(op2);
                break;
            case '\n':
                printf("\t%.8g\n", pop());
                break;
            default:
                printf("error: unknown command %s\n", s);
                break;
        }
    }
    return 0;
}

void push(double f) {
    if (sp < MAXVAL)
        val[sp++] = f;
    else
        printf("error:stack full, cant push %g\n", f);
}

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

void clearsp(void) { sp = 0; }

int getop(char s[]) {
    int i, c;

    while ((s[0] = c = getch()) == ' ' || c == '\t');
    s[1] = '\0';

    i = 0;
    if (islower(c)) {
        while (islower(s[++i] = c = getch()));;
        s[i] = '\0';
        if (c != EOF)
            ungetch(c);
        if (strlen(s) > 1)
            return NAME;
        else
            /*return c; this line was bad since when s < 1, the array s only has
            one character s[0], therofore, this character must be retorned in
            order to see if it is d,?,s etc. The character c instead contain
            whatever non-lower value wich always will result in a command
            uknown*/

            return s[0];
    }

    if (!isdigit(c) && c != '.' && c != '-')
        return c;

    if (c == '-')
        if (isdigit(c = getch()) || c == '.')
            s[++i] = c;
        else {
            if (c != EOF)
                ungetch(c);
            return '-';
        }

    if (isdigit(c))
        while (isdigit(s[++i] = c = getch()));

    if (c == '.')
        while (isdigit(s[++i] = c = getch()));

    s[i] = '\0';
    if (c != EOF)
        ungetch(c);
    return NUMBER;
}

int getch(void) { return (bufp > 0) ? buf[--bufp] : getchar(); }

void ungetch(int c) {
    if (bufp >= BUFSIZE)
        printf("ungetch: too many characters\n");
    else
        buf[bufp++] = c;
}

/* mathfnc: check the string s for supported math function */

void mathfnc(char s[]) {
    double op2;

    if (strcmp(s, "sin") == 0)
        push(sin(pop()));
    else if (strcmp(s, "cos") == 0)
        push(cos(pop()));
    else if (strcmp(s, "exp") == 0)
        push(exp(pop()));
    else if (strcmp(s, "pow") == 0) {
        op2 = pop();
        push(pow(pop(), op2));
    } else
        printf("error: %s is not supported\n", s);
}