To print the decimal value of a fraction.

#include <stdio.h>
/*
Copyright (c) 2020 Devine Lu Linvega
Permission to use, copy, modify, and distribute this software for any
purpose with or without fee is hereby granted, provided that the above
copyright notice and this permission notice appear in all copies.
THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
WITH REGARD TO THIS SOFTWARE.
*/
#define SZ 256
typedef struct Fraction {
int num, den;
} Fraction;
typedef struct Stack {
Fraction data[SZ];
Fraction *pointer;
} Stack;
typedef enum {
STANDARD,
MIXED,
DECIMAL,
HEXADECIMAL,
BINARY
} PrintMode;
PrintMode MODE;
/* helpers */
int
scmp(char *a, char *b)
{
int i = 0;
while(a[i] == b[i])
if(!a[i++])
return 1;
return 0;
}
int
gcd(int a, int b)
{
if(b == 0)
return a;
return gcd(b, a % b);
}
void
pbin(int n, unsigned int l)
{
while(l) {
putchar(n & l ? '1' : '0');
l >>= 1;
}
putchar(' ');
}
/* rpn */
int
error(char *err, char *msg)
{
printf("%s Error: %s\n", err, msg);
return 0;
}
int
trypop(Stack *s, int len)
{
int err = s->pointer - len < s->data;
if(err)
error("Stack", "underflow");
return !err;
}
int
trypush(Stack *s, int len)
{
int err = s->pointer + len >= s->data + SZ;
if(err)
error("Stack", "overflow");
return !err;
}
Fraction
pop(Stack *s)
{
return *(s->pointer--);
}
void
push(Stack *s, Fraction f)
{
*(++s->pointer) = f;
}
Fraction *
get(Stack *s, int offset)
{
return s->pointer - offset;
}
Fraction
Frac(int num, int den)
{
Fraction f;
int d = gcd(num, den);
f.num = num / d;
f.den = den / d;
return f;
}
void
print(Stack *s)
{
Fraction *f = s->data;
while(f++ != s->pointer) {
if(MODE == DECIMAL)
printf("%f ", f->num / (double)f->den);
else if(MODE == MIXED && f->num > f->den)
printf("%d&%d/%d ", f->num / f->den, f->num % f->den, f->den);
else if(MODE == HEXADECIMAL)
printf("%08hX ", f->num);
else if(MODE == BINARY)
pbin(f->num, 1 << 7);
else if(f->den != 1)
printf("%d/%d ", f->num, f->den);
else
printf("%d ", f->num);
}
printf("\n");
}
/* ops */
int
interpret(Stack *s, char *word)
{
int value;
if(!word[0] || word[0] == ' ' || word[0] == '.')
print(s);
else if(scmp(word, "std"))
MODE = STANDARD;
else if(scmp(word, "mix"))
MODE = MIXED;
else if(scmp(word, "dec"))
MODE = DECIMAL;
else if(scmp(word, "hex"))
MODE = HEXADECIMAL;
else if(scmp(word, "bin"))
MODE = BINARY;
else if(sscanf(word, "%d", &value) && trypush(s, 1))
push(s, Frac(value, 1));
/* stack */
else if(scmp(word, "pop") && trypop(s, 1))
pop(s);
else if(scmp(word, "clr"))
s->pointer = s->data;
else if(scmp(word, "swp") && trypop(s, 2)) {
Fraction b = pop(s);
Fraction a = pop(s);
push(s, Frac(b.num, b.den));
push(s, Frac(a.num, a.den));
} else if(scmp(word, "dup") && trypop(s, 1) && trypush(s, 1)) {
Fraction *f = get(s, 0);
push(s, Frac(f->num, f->den));
} else if(scmp(word, "ovr") && trypop(s, 2) && trypush(s, 1)) {
Fraction *f = get(s, 1);
push(s, Frac(f->num, f->den));
} else if(scmp(word, "rot") && trypop(s, 3)) {
Fraction c = pop(s);
Fraction b = pop(s);
Fraction a = pop(s);
push(s, Frac(b.num, b.den));
push(s, Frac(c.num, c.den));
push(s, Frac(a.num, a.den));
/* arithmetic */
} else if((word[0] == '+' || scmp(word, "add")) && trypop(s, 2)) {
Fraction b = pop(s);
Fraction a = pop(s);
push(s, Frac((a.num * b.den) + (a.den * b.num), a.den * b.den));
} else if((word[0] == '-' || scmp(word, "sub")) && trypop(s, 2)) {
Fraction b = pop(s);
Fraction a = pop(s);
push(s, Frac((a.num * b.den) - (a.den * b.num), a.den * b.den));
} else if((word[0] == '*' || scmp(word, "mul")) && trypop(s, 2)) {
Fraction b = pop(s);
Fraction a = pop(s);
push(s, Frac(a.num * b.num, a.den * b.den));
} else if((word[0] == '/' || scmp(word, "div")) && trypop(s, 2)) {
Fraction b = pop(s);
Fraction a = pop(s);
push(s, Frac(a.num * b.den, a.den * b.num));
} else if((word[0] == '%' || scmp(word, "mod")) && trypop(s, 2)) {
Fraction b = pop(s);
Fraction a = pop(s);
push(s, Frac((a.num * b.den) % (a.den * b.num), a.den * b.den));
/* bitwise */
} else if((word[0] == '&' || scmp(word, "and")) && trypop(s, 2)) {
Fraction b = pop(s);
Fraction a = pop(s);
push(s, Frac((a.num * b.den) & (a.den * b.num), a.den * b.den));
} else if((word[0] == '|' || scmp(word, "or")) && trypop(s, 2)) {
Fraction b = pop(s);
Fraction a = pop(s);
push(s, Frac((a.num * b.den) | (a.den * b.num), a.den * b.den));
} else if((word[0] == '^' || scmp(word, "xor")) && trypop(s, 2)) {
Fraction b = pop(s);
Fraction a = pop(s);
push(s, Frac((a.num * b.den) ^ (a.den * b.num), a.den * b.den));
} else if((scmp(word, "<<") || scmp(word, "rol")) && trypop(s, 2)) {
Fraction b = pop(s);
Fraction a = pop(s);
push(s, Frac((a.num * b.den) << (a.den * b.num), a.den * b.den));
} else if((scmp(word, ">>") || scmp(word, "ror")) && trypop(s, 2)) {
Fraction b = pop(s);
Fraction a = pop(s);
push(s, Frac((a.num * b.den) >> (a.den * b.num), a.den * b.den));
/* special */
} else if((scmp(word, "inv")) && trypop(s, 1)) {
Fraction f = pop(s);
push(s, Frac(f.den, f.num));
} else if(scmp(word, "vid") && trypop(s, 1) && trypush(s, 1)) {
Fraction f = pop(s);
push(s, Frac(f.num, 1));
push(s, Frac(f.den, 1));
} else if(word)
return error("Command", word);
return 1;
}
int
run(Stack *s)
{
int len = 0;
char c, word[64];
while((c = fgetc(stdin)) != EOF) {
if(c == ' ' || c == '\n') {
word[len] = '\0';
len = 0;
interpret(s, word);
} else
word[len++] = c;
}
return 0;
}
int
main()
{
Stack s;
s.pointer = s.data;
while(run(&s))
;
print(&s);
return 0;
}
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