Solve Exercise 5-2: getfloat()

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diff --git a/ch5/5-02_getfloat.c b/ch5/5-02_getfloat.c
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+#include <stdio.h>
+#include <math.h>
+
+/* The C Programming Language: 2nd Edition
+ *
+ * Exercise 5-2: Write getfloat, the floating-point analog of getint. What
+ * type does getfloat return as its function value?
+ *
+ * Answer: getfloat should return an integer, since getint's return value is
+ * only important to check its status, not the value type that it's working
+ * with. The only real "gotcha" here is making sure to use getch() after
+ * checking for a decimal point so the resulting loop will actually execute.
+ */
+
+#define BUFSIZE 100
+
+int getch(void);
+void ungetch(int);
+int getfloat(double *);
+
+char buf[BUFSIZE];
+int bufp = 0;
+
+int main() {
+	double foo;
+	double *bar = &foo;
+	while (getfloat(bar) > 0) {
+		printf("%f\n", foo);
+	}
+	return 0;
+}
+
+int getfloat(double *pn) {
+	int c, sign, places;
+
+	while (isspace(c = getch())) {
+	}
+	if (!isdigit(c) && c != EOF && c != '+' && c != '-') {
+		ungetch(c);
+		return 0;
+	}
+	sign = (c == '-') ? -1 : 1;
+	if (c == '+' || c == '-') {
+		c = getch();
+	}
+	if (c != '.' && !isdigit(c)) {
+		return 0;
+	}
+	for (*pn = 0.0; isdigit(c); c = getch()) {
+		*pn = 10.0 * *pn + (c - '0');
+	}
+	if (c == '.') {
+		c = getch(); // skip the decimal point or the loop won't trigger
+		for (places = -1; isdigit(c); c = getch()) {
+			*pn += (double)(c - '0') * pow(10, places--);
+		}
+	}
+	*pn *= sign;
+	if (c != EOF) {
+		ungetch(c);
+	}
+	return c;
+}
+
+int getch(void) {
+	return (bufp > 0) ? buf[--bufp] : getchar();
+}
+
+void ungetch(int c) {
+	if (bufp >= BUFSIZE) {
+		printf("ungetch: Too many characters.\n");
+	} else {
+		buf[bufp++] = c;
+	}
+}