Ex_4.3_rpn_modulus_negative.c

/* Adding the Modulus operator and provision for negative numbers 
* Program is given the input in a single and and it print the output upon
* getting a \n character.
* For e.g:
*
* 10 10 + 100 + 2 *
*		240
*/

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

#define MAXOP 100
#define NUMBER '0'

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

/* reverse polish calculator */

int main(void)
{
	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();
						if(op2 != 0.0)
							push(fmod(pop(),op2));
						else
							printf("erro:zero divisor\n");
						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, cant push %g\n",f);
}


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 != '.' && c != '-')
		return c;		// not a number
	i = 0;
	if (c == '-' || isdigit(c))    	// collect integer part along with '-'
		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);
	if (strcmp(s, "-") == 0)
		return '-';
	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;
}