Feature: Add First Challenge - Sum of N Natural Numbers, and Second Challenge - Decimal to Binary Conversion

README.md

@@ -154,6 +154,22 @@ Write a function called `celsiusToFahrenheit` that takes a temperature in Celsiu
 
 [Solution Explanation](./solutions/ch_16_Celsius_To_Fahrenheit/readme.md)
 
+## Challenge 17: Calculate the Sum of N Natural Number.
+
+Write a function that takes a number as input and returns sum from 1 to `n`. For example, if the input is 10, the function should return 55.
+
+Write a function called `getNaturalSum` that takes a number `n` as its parameter and returns sum of natural number.
+
+[Solution Explanation](./solutions/ch_17_Sum_Of_N_Natural_Number/readme.md)
+
+## Challenge 18: Convert Decimal to Binary.
+
+Write a function that takes a decimal number as input and returns binary string. For example, if the input is 12, the function should return 1100.
+
+Write a function called `decimalToBinary` that takes a decimal number as `decimal` in its parameter and returns binary string.
+
+[Solution Explanation](./solutions/ch_18_Decimal_To_Binary/readme.md)
+
 <!-- Add new challenges before this comment -->
 
 ## Contributors

solutions/ch_17_Sum_Of_N_Natural_Number/answer.js

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+// Function that calculates the sum of n natural number.
+function getNaturalSum(n) {
+    let sum = 0;   // Declare a sum variable to store the sum
+
+    // Running loop from 1 to n
+    for (let i = 1; i <= n; i++) {
+        // Adding the sum by i 
+        sum += i;  // sum = sum + i;   
+    }
+
+    return sum; // Return the sum
+}

solutions/ch_17_Sum_Of_N_Natural_Number/answer2.js

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+// Function that calculates the sum of n natural number.
+function getNaturalSum(n) {
+    // Using ternary operator (?:)
+    return n <= 1 ? n : n + getNaturalSum(n - 1);
+}

solutions/ch_17_Sum_Of_N_Natural_Number/readme.md

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+# Challenge 17: Calculate the Factorial of a Number.
+
+Write a function that takes a number as input and returns sum from 1 to `n`. For example, if the input is 10, the function should return 55.
+
+Write a function called `getNaturalSum` that takes a number `n` as its parameter and returns sum of natural number.
+
+## Answer 1
+
+```javascript
+// Function that calculates the sum of n natural number.
+function getNaturalSum(n) {
+  let sum = 0; // Declare a sum variable to store the sum
+
+  // Running loop from 1 to n
+  for (let i = 1; i <= n; i++) {
+    // Adding the sum by i
+    sum += i; // sum = sum + i;
+  }
+
+  return sum; // Return the sum
+}
+```
+
+## Answer 1 Explanation
+
+In the `getNaturalSum` function, declare `sum` variable to store the sum and initializing with 0 and then running a loop from 1 to `n` and adding the `sum` with all the numbers from 1 to `num`. After finishing the loop return the `sum`.
+
+## Answer 2 using Recursion
+
+```javascript
+// Function that calculates the sum of n natural number.
+function getNaturalSum(n) {
+    // Using ternary operator (?:)
+    return n <= 1 ? n : n + getNaturalSum(n - 1);
+}
+```
+
+## Answer 2 Explanation
+
+In the `getNaturalSum` function, checking value of `n` if `n` is more than 1 then adding `n` and return value of `getNaturalSum` with less than 1 `n` value. if value is less than or equal to 1 then it will return n, that value, and recursive function will return sum.
+
+Here is example how recursive function calculate factorial of 5:
+
+```JavaScript
+function getFactorial(num) {
+return 5 + getFactorial(4);
+            4 + getFactorial(3);
+                3 + getFactorial(2);
+                    2 + getFactorial(1);
+                        return 1;
+}
+```

solutions/ch_18_Decimal_To_Binary/answer.js

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+// Function to convert decimal numbers to binary strings
+function decimalToBinary(decimal) {
+    let binaryString = "";  // Initialize an empty string to store the binary digits
+
+    // Perform repeated division by 2 until the decimal number becomes 0
+    while (decimal > 0) {
+        // Append the remainder of division (0 or 1) to the binary string
+        binaryString = (decimal % 2) + binaryString;
+
+        // Update the decimal number by integer division (floor division) by 2
+        decimal = Math.floor(decimal / 2);
+    }
+
+    // Return the binary string
+    return binaryString;
+}

solutions/ch_18_Decimal_To_Binary/answer2.js

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+function decimalToBinary1(decimal) {
+    // Convert the decimal number to a binary string using the toString() method
+    let binaryString = decimal.toString(2);
+
+    // Return the binary string
+    return binaryString;
+}

solutions/ch_18_Decimal_To_Binary/readme.md

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+# Challenge 18: Convert Decimal to Binary.
+
+Write a function that takes a decimal number as input and returns binary string. For example, if the input is 12, the function should return 1100.
+
+Write a function called `decimalToBinary` that takes a decimal number as `decimal` in its parameter and returns binary string.
+
+## Answer 1
+
+```javascript
+// Function to convert decimal numbers to binary strings
+function decimalToBinary(decimal) {
+    let binaryString = "";  // Initialize an empty string to store the binary digits
+
+    // Perform repeated division by 2 until the decimal number becomes 0
+    while (decimal > 0) {
+        // Append the remainder of division (0 or 1) to the binary string
+        binaryString = (decimal % 2) + binaryString;
+
+        // Update the decimal number by integer division (floor division) by 2
+        decimal = Math.floor(decimal / 2);
+    }
+
+    // Return the binary string
+    return binaryString;
+}
+```
+
+## Answer 1 Explanation
+
+In the `decimalToBinary` function, declare `binaryString` variable to store the binary string with empty string and then running a while loop until decimal is greater than one. Inside loop adding remainder in `binaryString` and dividing `decimal` itself by 2. After finishing the loop return `binaryString`.
+
+## Answer 2 using toString()
+
+```javascript
+function decimalToBinary(decimal) {
+    // Convert the decimal number to a binary string using the toString() method
+    let binaryString = decimal.toString(2);
+
+    // Return the binary string
+    return binaryString;
+}
+```
+
+## Answer 2 Explanation
+
+`decimalToBinary` the built-in `toString()` method with a base argument of 2. This method directly converts the decimal number to a binary string.