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Exercise4-11.c
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Exercise4-11.c
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/*Exercise 4-11. Modify getop so that it doesn't need to use
ungetch. Hint: use an internal static variable.*/
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#define MAXOP 100 /* max size of operand or operator */
#define NUMBER '0'/* signal that a number was found */
int getop(char []);
void push(double);
double pop(void);
//pop and push
#define MAXVAL 100 /* maximum depth of val stack */
int sp = 0; /* next free stack position */
double val[MAXVAL]; /* value stack */
/* reverse Polish calculator */
int main()
{
int type;
double op2,op3;
char s[MAXOP];
int flag_p=0;
double recent=0;
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();
op3=pop();
if (op2>0.0&&op3>0.0)
push((int)op3 % (int)op2);
else
printf("Remainder of negative division");
break;
case 's': //s for sin
push(sin(pop()));
break;
case 'o': //o for cos
push(cos(pop()));
break;
case 't': //t for exp
push(exp(pop()));
break;
case 'p': //print last in stack
flag_p=1;
printf("\t%g\n",val[sp]);
break;
case 'd': //duplicate last in the sctak
flag_p=1;
sp++;
val[sp]=val[sp-1];
break;
case 'c': //exchage the last two values
flag_p=1;
sp++;
int aux=val[sp];
val[sp]=val[sp-1];
val[sp-1]=aux;
break;
case 'e': //clean stack "erase"
flag_p=1;
sp=0;
break;
case 'x': //x recent print value
push(recent);
break;
case 'w': //w pi
push(3.14);
break;
case '\n':
if(flag_p==0)
{
recent=pop();
printf("\t%.8g\n", recent);
}
else
flag_p=0;
break;
default:
printf("error: unknown command %s\n", s);
break;
}
}
return 0;
}
/* 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;
}
}
#include <ctype.h>
int getch(void);
void ungetch(int);
/* getop: get next character or numeric operand */
int getop(char s[])
{
int i, c;
static int ungetch_var='j';
if(ungetch_var==' '||ungetch_var=='\t'||ungetch_var=='j')
{
while ((s[0] = c = getch()) == ' ' || c == '\t')
;
s[1] = '\0';
}
if (!isdigit(c) && c != '.')
return c; /* not a number */
i = 0;
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_var=c; //saves no digit variable
return NUMBER;
}
#define BUFSIZE 100
char buf[BUFSIZE];/* buffer for ungetch */
int bufp = 0;/* next free position in buf */
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;
}