4-3-calculator-modulus.c

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

#define MAXOP   100
#define NUMBER  '0'

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

int main()
{
  int type;
  double 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 '\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 getop(char s[])
{
  int i, c;

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

  s[1] = '\0';

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

  i = 0;
  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;
}