feat(maths): added NumberOfDigits (TheAlgorithms#101)

* feat(maths): added NumberOfDigits

* fix: handled 0 input in NumberOfDigits

Author: T1LT

maths/number_of_digits.ts

@@ -0,0 +1,18 @@
+/**
+ * @function NumberOfDigits
+ * @description Calculate the number of digits of a natural number.
+ * @param {number} num - A natural number.
+ * @return {number} - Number of digits of given natural number.
+ * @see https://math.stackexchange.com/a/231745/518862
+ * @example NumberOfDigits(18) = 2
+ * @example NumberOfDigits(294568) = 6
+ * @example NumberOfDigits(128798319794) = 12
+ */
+
+export const NumberOfDigits = (num: number): number => {
+  if (num <= 0 || !Number.isInteger(num)) {
+    throw new Error("only natural numbers are supported");
+  }
+
+  return Math.floor(Math.log10(num)) + 1;
+};

maths/test/number_of_digits.test.ts

@@ -0,0 +1,19 @@
+import { NumberOfDigits } from "../number_of_digits";
+
+describe("NumberOfDigits", () => {
+  test.each([-890, -5.56, -7, 0, 0.73, 4.2, NaN, -Infinity, Infinity])(
+    "should throw an error for non natural number %d",
+    (num) => {
+      expect(() => NumberOfDigits(num)).toThrowError(
+        "only natural numbers are supported",
+      );
+    },
+  );
+
+  test.each([[1, 1], [18, 2], [549, 3], [7293, 4], [1234567890, 10]])(
+    "of %i should be %i",
+    (num, expected) => {
+      expect(NumberOfDigits(num)).toBe(expected);
+    },
+  );
+});