four/getop.c


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#include <stdio.h>
#include <ctype.h>

#define NUMBER '0'

int getch(void);
void ungetch(int);

/* get next operator or numeric operand */
int
getop(char s[])
{
	int i, c;

	while((s[0] = c = getch()) == ' ' || c == '\t');
	s[1] = '\0';
	/* not a number */
	if (!isdigit(c) && c != '.') {
		return c;
	}
	i = 0;
	/* collect integer part */
	if (isdigit(c)) {
		while (isdigit(s[++i] = c = getch()));
	}
	/* collect fraction part */
	if (c == '.') {
		while (isdigit(s[++i] = c = getch()));
	}
	s[i] = '\0';
	if (c != EOF) {
		ungetch(c);
	}
	return NUMBER;
}