1 files changed, 161 insertions, 0 deletions
diff --git a/5.12.c b/5.12.c
new file mode 100644
index 0000000..5c66060
--- /dev/null
+++ b/5.12.c
@@ -0,0 +1,161 @@
+#include <stdio.h>
+#include <ctype.h>
+
+#define DEFTAB 8
+#define MAXSTOPS 65
+#define ON 1
+
+int stops[MAXSTOPS];
+int stop_position, m, n;
+
+void entab(void);
+void detab(void);
+
+int 
+main(int argc, char **argv)
+{
+  char flag;
+  int detab_bool = 0, entab_bool = 0, mnloop_bool = 0;
+
+  while (--argc > 0 && (**++argv == '-' || **argv == '+'))
+    while((flag = *++*argv))
+      switch (flag) {
+        case 'e' :
+          entab_bool = ON;
+          break;
+        case 'd' :
+          detab_bool = ON;
+          break;
+        case 's' :
+          if(*++*argv != '=')
+            argc = -1;
+          else 
+            (*argv)++;
+
+          if (**argv == '\0')
+            argc = -1;
+
+          while (isdigit(**argv)) {
+            if (stop_position > MAXSTOPS)
+              argc = -1;
+
+            stops[stop_position] = stops[stop_position] * 10 + (**argv) - '0';
+            (*argv)++;
+            if (**argv == ',') {
+              (*argv)++;
+              if(isdigit(**argv) && stop_position < MAXSTOPS)
+                stop_position++;
+            }
+          }
+          stop_position++;
+
+          (*argv)--;
+          break;
+        default :
+          if (isdigit(flag)) {
+            if (*(*argv - 1) == '+')
+              for (mnloop_bool = 1; isdigit(**argv); (*argv)++)
+                n = n * 10 + (**argv) - '0';
+            else if (*(*argv - 1) == '-')
+              for (mnloop_bool = 1; isdigit(**argv); (*argv)++)
+                m = m * 10 + (**argv) - '0'; 
+            
+            if(mnloop_bool) {
+              (*argv)--;
+              mnloop_bool = 0;
+            }
+          } 
+
+          else {
+            argc = -1;
+            printf("Err: illigal option %c\n", flag);
+          }
+          
+          break;
+      }
+
+  if (argc || !entab_bool ^ detab_bool || !m != !n)
+    printf("Usage: tab (-e || -d) (-s=s1,s2,s3,...,s%d || -m +n)\n", MAXSTOPS-1);
+  else if(entab_bool)
+    entab();
+  else if (detab_bool)
+    detab();
+
+  return 0;
+}
+
+void 
+entab(void)
+{
+  char input;
+  int space, stop_now, count;
+
+  count = 0;
+  space = 0;
+  stop_now = 0;
+  stops[stop_position] = DEFTAB; 
+
+  while((input = getchar()) != EOF)
+    switch(input) {
+      case ' ' :
+        space++;
+        count++;
+        break;
+      case '\n' :
+        count = 0;
+        break;
+      default :
+        if (count >= m)
+          stops[stop_position] = m;
+
+        while (space/stops[stop_now]) {
+          space -= stops[stop_now];
+
+          putchar('\t');
+
+          if (stop_now < stop_position)
+            stop_now++;
+        }
+
+        while (space) {
+          putchar(' ');
+          space--;
+        }
+
+        putchar(input);
+        break;
+    }
+}
+
+void 
+detab(void)
+{
+  char input; 
+  int count, space, stop_now;
+
+  count = 0;
+  stop_now = 0;
+  stops[stop_position] = DEFTAB; 
+
+  while ((input = getchar()) != EOF)
+    switch (input) {
+      case '\n' :
+        count = 0;
+        putchar('\n');
+        break;
+      case '\t' :
+        space = stops[stop_now] - count%stops[stop_now];
+        count += space;
+        while (space--)
+          putchar(' ');
+        if (stop_now < stop_position)
+          stop_now++;
+        break;
+      default :
+        if (count++ >= m)
+          stops[stop_position] = n;
+
+        putchar(input);
+        break;
+    }
+}