//WIP

Author: satyajitghana

Chapter-6/Exercise 6-4/buffer.c

@@ -0,0 +1,22 @@
+#include <stdio.h>
+#include <string.h>
+#define BUFSIZE 100
+
+int buf[BUFSIZE]; /* buffer for ungetch */
+int bufp = 0; /* buffer pointer (not a real pointer) */
+
+int getch(void) /* get a (possibly pushed back) character */ {
+    return (bufp > 0) ? buf[--bufp] : getchar();
+}
+
+void ungetch(int c) /* push character back on input */ {
+    if (bufp >= BUFSIZE)
+        printf("ungetch : too many characters\n");
+    else
+        buf[bufp++] = c;
+}
+
+void ungets(char s[]) /* push string s back to input */ {
+    int i = strlen(s);
+    while (i > 0) ungetch(s[--i]);
+}

Chapter-6/Exercise 6-4/buffer.h

@@ -0,0 +1,10 @@
+#ifndef BUFFER_H
+#define BUFFER_H
+
+int getch(void);
+
+void ungetch(int);
+
+void ungets(char []);
+
+#endif

Chapter-6/Exercise 6-4/io.c

@@ -0,0 +1,51 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <ctype.h>
+#include "buffer.h"
+#include "io.h"
+
+char *_strdup(char *s) { /* make a duplicate of s */
+    char *p;
+
+    p = (char *) malloc(strlen(s) + 1); /* +1 for '\0' */
+    if (p != NULL)
+        strcpy(p, s);
+    return p;
+}
+
+/* _strndup: make a duplicate of at most 6 characters of s*/
+char *_strndup(char *s, int n) {
+    char *p;
+
+    p = (char *) malloc(n +1);
+    if (p != NULL)
+        strncpy(p, s, n);
+    return p;
+}
+
+/* getword: get next word or character from input */
+int getword(char *word, int lim) {
+    int c;
+    char *w = word;
+
+    /* skip the whitespaces */
+    while (isspace(c = getch()))
+        ;
+    if (c != EOF)
+        *w++ = c;
+    if (!isalpha(c)) {
+        *w = '\0';
+        return c;
+    }
+
+    while (--lim) {
+        if (!isalnum(*w = getch())) {
+            ungetch(*w);
+            break;
+        }
+        w++;
+    }
+    *w = '\0';
+    return word[0];
+}

Chapter-6/Exercise 6-4/io.h

@@ -0,0 +1,9 @@
+#ifndef IO_H
+#define IO_H
+
+char *_strdup(char *s);
+char *_strndup(char *s, int n);
+
+int getword(char *word, int lim);
+
+#endif

Chapter-6/Exercise 6-4/main.c

@@ -0,0 +1,23 @@
+#include <stdio.h>
+#include <ctype.h>
+#include <stdlib.h>
+#include <string.h>
+#include "tree.h"
+#include "io.h"
+
+#define MAXWORD 100
+
+int getword(char *, int);
+
+/* word frequency count */
+int main(int argc, char **argv) {
+    struct tnode *root;
+    char word[MAXWORD];
+
+    root = NULL;
+    while (getword(word, MAXWORD) != EOF)
+        if (isalpha(word[0]))
+            root = addtree(root, word);
+    treeprint(root);
+    return 0;
+}

Chapter-6/Exercise 6-4/tree.c

@@ -0,0 +1,37 @@
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+#include "io.h"
+#include "tree.h"
+
+/* addtree: add a node with w, at or below p */
+struct tnode *addtree(struct tnode *p, char *w) {
+    int cond;
+
+    if (p == NULL) {    /* a new word has arrived */
+        p = talloc();
+        p -> word = _strdup(w);
+        p -> count = 1;
+        p -> left = p -> right = NULL;
+    } else if ((cond = strcmp(w, p -> word)) == 0)
+        p -> count++; /* repeated word */
+    else if (cond < 0)
+        p -> left = addtree(p -> left, w);
+    else
+        p -> right = addtree(p -> right, w);
+    return p;
+}
+
+/* treeprint: in-order print of tree p */
+void treeprint(struct tnode *p) {
+    if (p != NULL) {
+        treeprint(p -> left);
+        printf("%4d %s\n", p -> count, p -> word);
+        treeprint(p -> right);
+    }
+}
+
+/* talloc: make a tnode */
+struct tnode *talloc(void) {
+    return (struct tnode *) malloc(sizeof(struct tnode));
+}

Chapter-6/Exercise 6-4/tree.h

@@ -0,0 +1,17 @@
+#ifndef TREE_H
+#define TREE_H
+
+struct tnode {          /* the tree node: */
+    char *word;             /* points to the text   */
+    int count;              /* number of occurences */
+    struct tnode *left;     /* left child           */
+    struct tnode *right;    /* right child          */
+};
+
+struct tnode *addtree(struct tnode *, char *);
+
+void treeprint(struct tnode *p);
+
+struct tnode *talloc(void);
+
+#endif