decimal to binary using recursion (TheAlgorithms#575)

* add decimal_to_binary_recursion.c

* updating DIRECTORY.md

Co-authored-by: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>

DIRECTORY.md

@@ -12,6 +12,7 @@
   * [Binary To Octal](https://github.com/TheAlgorithms/C/blob/master/conversions/binary_to_octal.c)
   * [C Atoi Str To Integer](https://github.com/TheAlgorithms/C/blob/master/conversions/c_atoi_str_to_integer.c)
   * [Decimal To Binary](https://github.com/TheAlgorithms/C/blob/master/conversions/decimal_to_binary.c)
+  * [Decimal To Binary Recursion](https://github.com/TheAlgorithms/C/blob/master/conversions/decimal_to_binary_recursion.c)
   * [Decimal To Hexa](https://github.com/TheAlgorithms/C/blob/master/conversions/decimal_to_hexa.c)
   * [Decimal To Octal](https://github.com/TheAlgorithms/C/blob/master/conversions/decimal_to_octal.c)
   * [Decimal To Octal Recursion](https://github.com/TheAlgorithms/C/blob/master/conversions/decimal_to_octal_recursion.c)

conversions/decimal_to_binary_recursion.c

@@ -0,0 +1,38 @@
+/**
+ * @file
+ * @brief Convert decimal to binary using recursion algorithm
+ */
+#include <assert.h>
+
+/**
+ * Decimal to binary using recursion algorithm.
+ * For example, if number = 5, the function returns the decimal integer 101.
+ * @param number positive integer number to convert
+ * @returns integer with digits representing binary value representation of
+ * number.
+ */
+int decimal_to_binary(unsigned int number)
+{
+    return number == 0 ? 0 : number % 2 + 10 * decimal_to_binary(number / 2);
+}
+
+/** Test function */
+void test()
+{
+    const int sets[][2] = {
+        {0, 0}, {1, 1}, {2, 10}, {3, 11}, {4, 100}, {6, 110}, {7, 111},
+        /* add more data sets to test */
+    };
+
+    for (int i = 0, size = sizeof(sets) / sizeof(sets[0]); i < size; ++i)
+    {
+        assert(decimal_to_binary(sets[i][0]) == sets[i][1]);
+    }
+}
+
+/** Driver Code */
+int main()
+{
+    test();
+    return 0;
+}