diff --git a/The C Programming Language/1.20.c b/The C Programming Language/1.20.c
new file mode 100644
index 0000000..9db3a33
--- /dev/null
+++ b/The C Programming Language/1.20.c	
@@ -0,0 +1,72 @@
+#include <stdio.h>
+
+int _getline(char s[], int lim)
+{
+	int c, i, j;
+	for (i = 0; (c = getchar()) != '\n'; ++i)
+	{
+		if (i < lim - 1)
+			s[i] = c;
+	}
+
+	j = i;
+	if (j > lim - 1)
+		j = lim - 1;
+	s[j] = '\0';
+	return j - 1;
+}
+
+void entab(char to[], char from[], int columns)
+{
+	int is_placing_spaces = 0;
+	int remaining_spaces = columns;
+	int i_to = 0;
+	int i_from = 0;
+
+	while (from[i_from] != '\0')
+	{
+		if (from[i_from] == '\t')
+			is_placing_spaces = 1;
+		
+		if (is_placing_spaces)
+		{
+			if (remaining_spaces == 0)
+			{
+				is_placing_spaces = 0;
+				remaining_spaces = columns + 1;
+				++i_from;
+			}
+			else
+			{
+				to[i_to] = '_';
+				++i_to;
+			}
+		}
+		else
+		{
+			if (remaining_spaces == 0)
+				remaining_spaces = columns;
+
+			to[i_to] = from[i_from];
+			++i_to;
+			++i_from;
+		}
+
+		--remaining_spaces;
+	}
+
+	to[i_to] = '\0';
+}
+
+main()
+{
+	int size = 500;
+	char from[size];
+	char to[size];
+	while (1)
+	{
+		_getline(from, size);
+		entab(to, from, 4);
+		printf("%s\n", to);
+	}
+}