Initial commit

This is a scanf and sscanf version of getop.

Author: fsaadatmand

chapter07/7-5a.c

@@ -0,0 +1,123 @@
+/*
+ * Exercise 7-5. Rewrite the postfix calculator of Chapter 4 to use scanf
+ * and/or sscanf to do the input and number conversion.
+ *
+ * Note:  scanf and sscanf version
+ *
+ * Faisal Saadatmand
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#define MAXOP    100                   /* max size of operand or operator */
+#define NUMBER   '0'                   /* signal that a number was found */
+#define MAXVAL   100                   /* maximum depth of val stack */
+#define BUFSIZE  100
+
+/* functions */
+void push(double);
+double pop(void);
+int getop(double *);
+void ungetns(char *, int );
+
+/* globals */
+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("error: stack empty\n");
+		return 0.0;
+	}
+}
+
+/* getop: get next operator or numeric operand - scanf and sscanf version */
+int getop(double *number)
+{
+	char c;
+	int n;                     /* number of reaf characters */
+	static char s[MAXOP];
+
+	if (scanf("%c", &c) < 0)
+		return EOF;
+
+	if (c == '\n')
+		return c;
+
+	ungetc(c, stdin);
+	scanf("%s", s);            /* parse string from input stream */
+	if (!sscanf(s, "%lf %n", number, &n)) { /* match number from string */
+		sscanf(s, "%c", &c);   /* not a number */
+		if (strlen(s) > 1)     /* check for unread characters */
+			ungetns(s, 1);
+		return c;
+	}
+	
+	if (n != (int) strlen(s))  /* check unread char from match */
+		ungetns(s, n);
+
+	return NUMBER;
+}
+
+/* ungetns: push back a string starting at position n onto input stream */
+void ungetns(char *s, int n)
+{
+	int i;
+
+	for (i = strlen(s) - 1 ; i >= n; --i)
+		ungetc(s[i], stdin);
+}
+
+/* reverse polish calculator - scanf/sscanf version */
+int main(void)
+{
+	int type;
+	double op2, op;
+
+	while ((type = getop(&op)) != EOF) {
+		switch (type) {
+		case (NUMBER):
+			push(op);
+			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 division\n");
+			break;
+		case '\n':
+			printf("\t%.8g\n", pop());
+			break;
+		default:
+			printf("error: unknown command %c\n", type);
+			break;
+		}
+	}
+	return 0;
+}