examples

commit d288884d5c590400d18c23d0fb6839cfd6112d5a
parent f3fdc205176881e8c2cb70fa29cdb14d4e9711ef
Author: Henry Wilson <henry@henryandlizzy.uk>
Date:   Sat, 26 Aug 2023 17:42:57 +0100

damm-checksum: Add checksumming program example

Diffstat:
A
src/damm-checksum.c
 | 
58
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

1 file changed, 58 insertions(+), 0 deletions(-)
diff --git a/src/damm-checksum.c b/src/damm-checksum.c
@@ -0,0 +1,58 @@
+#include <stdio.h>
+#include <ctype.h>
+#include <stdlib.h>
+#include <string.h>
+
+char damm_sum(char const* const str)
+{
+	static char const lookup[100] = {
+		0, 3, 1, 7, 5, 9, 8, 6, 4, 2,
+		7, 0, 9, 2, 1, 5, 4, 8, 6, 3,
+		4, 2, 0, 6, 8, 7, 1, 3, 5, 9,
+		1, 7, 5, 0, 9, 8, 3, 4, 2, 6,
+		6, 1, 2, 3, 0, 4, 5, 9, 7, 8,
+		3, 6, 7, 4, 2, 0, 9, 5, 8, 1,
+		5, 8, 6, 9, 7, 2, 0, 1, 3, 4,
+		8, 9, 4, 5, 3, 6, 2, 0, 1, 7,
+		9, 4, 3, 8, 6, 1, 7, 2, 0, 5,
+		2, 5, 8, 1, 4, 3, 6, 7, 9, 0,
+	};
+	int last = 0;
+	char const* c = str;
+
+	while (isdigit(*c))
+		last = lookup[*c++ - '0' + last * 10];
+
+	if (!*c)
+		return last + '0';
+
+	dprintf(2, "'%s' must contain only digits\n", str);
+	exit(1);
+}
+
+void damm_append(char const* str)
+{
+	printf("%s%c\n", str, damm_sum(str));
+}
+
+int damm_check(char const* str)
+{
+	return damm_sum(str) == '0';
+}
+
+int main(int, char* argv[])
+{
+	++argv;
+
+	for (/**/; *argv; ++argv)
+	{
+		if (!strcmp(*argv, "-c"))
+		{
+			++argv;
+			break;
+		}
+		damm_append(*argv);
+	}
+	for (/**/; *argv; ++argv)
+		printf("%s: %s\n", *argv, damm_check(*argv) ? "OK" : "BAD");
+}