diff --git a/c/qrcodegen.c b/c/qrcodegen.c
index bf30444..c7df95d 100644
--- a/c/qrcodegen.c
+++ b/c/qrcodegen.c
@@ -25,6 +25,7 @@
 #include <assert.h>
 #include <stdint.h>
 #include <string.h>
+#include "qrcodegen.h"
 
 
 /*---- Forward declarations for private functions ----*/
@@ -37,6 +38,41 @@ static uint8_t finiteFieldMultiply(uint8_t x, uint8_t y);
 
 /*---- Function implementations ----*/
 
+bool qrcodegen_isAlphanumeric(const char *text) {
+	for (; *text != '\0'; text++) {
+		char c = *text;
+		if (('0' <= c && c <= '9') || ('A' <= c && c <= 'Z'))
+			continue;
+		else switch (c) {
+			case ' ':
+			case '$':
+			case '%':
+			case '*':
+			case '+':
+			case '-':
+			case '.':
+			case '/':
+			case ':':
+				continue;
+			default:
+				return false;
+		}
+		return false;
+	}
+	return true;
+}
+
+
+bool qrcodegen_isNumeric(const char *text) {
+	for (; *text != '\0'; text++) {
+		char c = *text;
+		if (c < '0' || c > '9')
+			return false;
+	}
+	return true;
+}
+
+
 // Calculates the Reed-Solomon generator polynomial of the given degree, storing in result[0 : degree].
 static void calcReedSolomonGenerator(int degree, uint8_t result[]) {
 	// Start with the monomial x^0
diff --git a/c/qrcodegen.h b/c/qrcodegen.h
new file mode 100644
index 0000000..c85765f
--- /dev/null
+++ b/c/qrcodegen.h
@@ -0,0 +1,39 @@
+/* 
+ * QR Code generator library (C)
+ * 
+ * Copyright (c) Project Nayuki
+ * https://www.nayuki.io/page/qr-code-generator-library
+ * 
+ * (MIT License)
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to
+ * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
+ * the Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ * - The above copyright notice and this permission notice shall be included in
+ *   all copies or substantial portions of the Software.
+ * - The Software is provided "as is", without warranty of any kind, express or
+ *   implied, including but not limited to the warranties of merchantability,
+ *   fitness for a particular purpose and noninfringement. In no event shall the
+ *   authors or copyright holders be liable for any claim, damages or other
+ *   liability, whether in an action of contract, tort or otherwise, arising from,
+ *   out of or in connection with the Software or the use or other dealings in the
+ *   Software.
+ */
+
+#pragma once
+
+#include <stdbool.h>
+
+
+/* 
+ * Tests whether the given string can be encoded in alphanumeric mode.
+ */
+bool qrcodegen_isAlphanumeric(const char *text);
+
+
+/* 
+ * Tests whether the given string can be encoded in numeric mode.
+ */
+bool qrcodegen_isNumeric(const char *text);