4-5-calculator-math.c

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

#define MAXOP   100
#define NUMBER  '0'
#define PRINT   '1'
#define SWAP    '2'
#define SIN     '3'
#define EXP     '4'
#define POW     '5'

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

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

  while ((type = getop(s)) != EOF) {
    switch (type) {
      case NUMBER:
        push(atof(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();
        push((int) pop() % (int) op2);
        break;
      case SIN:
        push(sin(pop()));
        break;
      case EXP:
        push(exp(pop()));
        break;
      case POW:
        op2 = pop();
        push(pow(pop(), op2));
        break;
      case PRINT: // print top of stack
        op1 = pop();
        push(op1);
        printf("top of stack: %.8g\n", op1);
        break;
      case SWAP: // swap top values
        op2 = pop();
        op1 = pop();
        push(op2);
        push(op1);
        break;
      case '\n':
        printf("\t%.8g\n", pop());
        break;
      default:
        printf("error: unknown command %s\n", s);
        break;
    }
  }

  return 0;
}

#define MAXVAL  100

int sp = 0;
double val[MAXVAL];

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

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

#include <ctype.h>

int getch(void);
void ungetch(int);

int getstr(char str[])
{
  int i, c;

  for (i = 0; str[i] != '\0'; i++) {
    if ((c = getch()) == str[i]) {
      //printf("expected %c and got %c\n", c, str[i]);
      continue;
    } else {
      //printf("expected %c but got %c\n", c, str[i]);
      ungetch(c); // unget non-matching char
      for (i-- ; i >= 0; i--) { // unget previously matched chars
        ungetch(str[i]);
      }
      return 0;
    }
  }

  return 1;
}

int getop(char s[])
{
  int i, c, c2;

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

  s[1] = '\0';

  if (islower(c)) {
    if (!islower(c2 = getch())) {
      ungetch(c2);
      return s[0]; // single char identifier
    }
    ungetch(c2);
    ungetch(c);

    if (getstr("print"))
      return PRINT;
    else if (getstr("swap"))
      return SWAP;
    else if (getstr("sin"))
      return SIN;
    else if (getstr("exp"))
      return EXP;
    else if (getstr("pow"))
      return POW;
    else
      return -1;
  } else {
    i = 0;

    if (!isdigit(c) && c != '.')
      return c; // not a number

    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;
  }
}

#define BUFSIZE   100

char buf[BUFSIZE];
int bufp = 0;

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;
}