Left off on exercise 1.23

ch_01/exercise_01-20/main.c

@@ -0,0 +1,88 @@
+/*
+ *
+ * Exercise 1-20. Write a program detab that replaces the tabs in the input with the
+ * proper number of blanks to space to the next tab stop. Assume a fixed set of tab
+ * stops, say every n columns. Should n be a variable or a symbolic parameter?
+ *
+ * Author: Kun Deng
+ */
+
+#include <stdio.h>
+
+#define TAB_REPRESENTER 2 // Represents how many spaces a tab would equal
+#define LINE_MAX_LIMIT 1000
+
+char line[LINE_MAX_LIMIT];
+int line_length;
+
+int get_line(void);
+
+void replace_tabs(void);
+
+
+int main()
+{
+    extern int line_length;
+
+    printf("Enter a sequence of characters\n");
+    printf("Any tabs will be replaced with %d white space characters\n", LINE_MAX_LIMIT);
+
+    while (line_length = get_line())
+    {
+        printf("before: %s\n", line);
+        replace_tabs();
+        printf("after: %s\n", line);
+    }
+
+    return 0;
+}
+
+
+int get_line(void)
+{
+    extern char line[];
+    int i = 0;
+    int c;
+
+    for (; (c = getchar()) != EOF && c != '\n'; ++i)
+    {
+        line[i] = c;
+    }
+
+    line[i] = '\0';
+
+    return i;
+}
+
+
+void replace_tabs(void)
+{
+    extern char line[];
+    extern int line_length;
+
+    for (int i = 0; i != line_length; ++i)
+    {
+        char some_char = line[i];
+
+        if (some_char == '\t')
+        {
+            int new_line_length = line_length + TAB_REPRESENTER;
+
+            line[new_line_length] = '\0';
+
+            for (int j = (line_length - 1); j > i; --j)
+            {
+                line[j + TAB_REPRESENTER] = line[j];
+            }
+
+            for (int k = i; k < (i + TAB_REPRESENTER); ++k)
+            {
+                line[k] = ' ';
+            }
+
+            line_length = new_line_length;
+
+            line[i + TAB_REPRESENTER] = 127;
+        }
+    }
+}