Exercise 6.1

Working on exercise 6.1. Setting up the code before starting. Functions are being used that were deinfed in earlier chapters - chapter 4.

ch_06/exercise_06-01/main.c

@@ -0,0 +1,128 @@
+/*
+ *
+ * Exercise 6-1. Our version of getword does not properly handle underscores,
+ * string constants, comments, or preprocessor control lines. Write a
+ * better version.
+ *
+ * Author: Kun Deng
+ */
+
+#include <stdio.h>
+#include <ctype.h>
+#include <string.h>
+#include <stddef.h>
+
+#define BUFFSIZE 100
+#define MAXWORD 100
+
+#define NKEYS (sizeof keytab / sizeof(struct key))
+
+char buf[BUFFSIZE];
+int bufp = 0;
+
+struct key {
+    char *word;
+    int count;
+};
+
+/*
+struct key {
+    char *word;
+    int count;
+} keytab[NKEYS];
+*/
+
+struct key keytab[] = {
+    "auto", 0,
+    "break", 0,
+};
+
+
+/* getword: get next word or character from input */
+int getword(char *word, int lim);
+
+/* binsearch: find word in tab[0]...tab[n-1] */
+struct key *binsearch(char *word, struct key *tab, int n);
+
+/* get a (possibly pushed back) character */
+int getch(void);
+
+/* push character back on input */
+void ungetch(int c);
+
+
+int getword(char *word, int lim) {
+    int c, getch(void);
+    void ungetch(int);
+    char *w = word;
+
+    while (isspace(c = getch()));
+
+    if (c != EOF)
+        *w++ = c;
+    if (!isalpha(c)) {
+        *w = '\0';
+        return 0;
+    }
+
+    for (; --lim > 0; w++)
+        if (!isalnum(*w = getch())) {
+            ungetch(*w);
+            break;
+        }
+
+    *w = '\0';
+    return word[0];
+}
+
+struct key *binsearch(char *word, struct key *tab, int n) {
+    int cond;
+    struct key *low = &tab[0];
+    struct key *high = &tab[n];
+    struct key *mid;
+
+    while (low < high) {
+        mid = low + (high-low) / 2;
+        if ((cond = strcmp(word, mid->word)) < 0 )
+            high = mid;
+        else if (cond > 0 )
+            low = mid + 1;
+        else
+            return mid;
+    }
+
+    return NULL;
+}
+
+int getch(void) {
+    return (bufp > 0) ? buf[--bufp] : getchar();
+}
+
+
+/* push character back on input */
+void ungetch(int c) {
+    if (bufp >= BUFFSIZE)
+        printf("ungetch: too many characters\n");
+    else
+        buf[bufp++] = c;
+}
+
+
+int main()
+{
+    int n;
+    char word[MAXWORD];
+    struct key *p;
+
+    while (getword(word, MAXWORD) != EOF)
+        if (isalpha(word[0]))
+            if ((p = binsearch(word, keytab, NKEYS)) >= 0)
+                p->count++;
+
+    for (p = 0; p < keytab + NKEYS; p++)
+        if (p->count > 0)
+            printf("%4d %s\n", p->count, p->word);
+
+
+    return 0;
+}