From 70aedfed18efdb01ef1727a0bbf048fac65c77c3 Mon Sep 17 00:00:00 2001
From: Zhineng Li <im@zhineng.li>
Date: Wed, 4 Feb 2026 12:55:36 +0800
Subject: ch01-19: reverse the caracter string s

---
 ch01/ex19-reverse.c | 56 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 56 insertions(+)
 create mode 100644 ch01/ex19-reverse.c

(limited to 'ch01')

diff --git a/ch01/ex19-reverse.c b/ch01/ex19-reverse.c
new file mode 100644
index 0000000..7179290
--- /dev/null
+++ b/ch01/ex19-reverse.c
@@ -0,0 +1,56 @@
+#include <stdio.h>
+#define MAXLINE 1000	/* maximum input line size */
+
+int getln(char line[], int maxline);
+void reverse(char to[], char from[], int len);
+
+/* reverse the input line */
+int main()
+{
+	int len;	/* current line length */
+	char line[MAXLINE];	/* current input line */
+	char rline[MAXLINE];	/* reversed line */
+
+	while ((len = getln(line, MAXLINE)) > 0) {
+		reverse(rline, line, len);
+		printf("%s", rline);
+	}
+
+	return 0;
+}
+
+/* getln:  read a line into s, return length */
+int getln(char s[], int lim)
+{
+	int c, i;
+
+	for (i=0; i<lim-1 && (c=getchar())!=EOF && c!='\n'; ++i)
+		s[i] = c;
+	if (c == '\n') {
+		s[i] = c;
+		++i;
+	}
+	s[i] = '\0';
+	return i;
+}
+
+/* reverse:  reverse the string */
+void reverse(char to[], char from[], int len)
+{
+	int i, nl = 0;
+
+	if (from[len-1] == '\n') {
+		nl = 1;
+		--len;
+	}
+
+	for (i=0; i < len; ++i)
+		to[i] = from[len-i-1];
+
+	if (nl == 1) {
+		to[i] = '\n';
+		++i;
+	}
+
+	to[i] = '\0';
+}
-- 
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