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exercise4-3.c
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exercise4-3.c
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#include <stdio.h>
#include <stdlib.h> // for atof()
#include <math.h> // for remainder(x,y)
#define MAXOP 100 // max size of operand or operator
#define NUMBER '0'
int getop(char []);
void push(double);
double pop(void);
void showInternals(int);
//reverse polish calculator
int main(){
int type;
double op2;
char s[MAXOP];
while((type = getop(s)) != EOF) {
showInternals(type);
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(remainder(pop(), op2));
else
printf("error: zero modulus\n");
break;
case '\n':
printf("\tResult: %.8g\n", pop());
break;
default:
printf("error: unknown command %s\n", s);
break;
}
}
return 0;
}
#define MAXVAL 100 // maximum depth of val stack
int sp = 0; // next free stack position
double val[MAXVAL]; // value stack
// 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("pop error: stack empty.\n");
return 0.0;
}
}
#include <ctype.h>
int getch(void);
void ungetch(int);
// getop: get next operator or numeric operand
// separate inputs with either space or tab
int getop(char s[]){
int i, c;
while((s[0] = c = getch()) == ' ' || c == '\t')
; // ignore
s[1] = '\0';
if (!isdigit(c) && c != '.' && c != '-')
return c; // not a number
i = 0;
if(isdigit(c) || c == '-') // collect integer part
while(isdigit(s[++i] = c = getch()))
;
if(c == '.') // collect fractional part
while (isdigit(s[++i] = c = getch()))
;
s[i] = '\0';
if( c != EOF)
ungetch(c);
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;
}
void showInternals(int type)
{
int i;
printf("Operation: %c\tstack:\t", type == NUMBER ? ' ' : type);
for(i = 0; i < sp; i++)
printf("%lf, ", val[i]);
printf("\n\n");
}