diff --git a/1-exercises/A-undefined/exercise.js b/1-exercises/A-undefined/exercise.js
index 0acfc78d..bec36e60 100644
--- a/1-exercises/A-undefined/exercise.js
+++ b/1-exercises/A-undefined/exercise.js
@@ -11,26 +11,23 @@
 
 // Example 1
 let a;
-console.log(a);
-
+console.log(a); // a is declared as a variable. But no value has been assigned
 
 // Example 2
 function sayHello() {
-    let message = "Hello";
+  let message = "Hello"; //  This function does not return anything, so definition is not enough.
 }
 
 let hello = sayHello();
-console.log(hello);
-
+console.log(hello); // Variable defined but function must be defined too.
 
 // Example 3
 function sayHelloToUser(user) {
-    console.log(`Hello ${user}`);
+  console.log(`Hello ${user}`);
 }
 
-sayHelloToUser();
-
+sayHelloToUser(); // user declared as a parameter. But when calling a function, an argument is needed not to get undefined result
 
 // Example 4
-let arr = [1,2,3];
-console.log(arr[3]);
+let arr = [1, 2, 3];
+console.log(arr[3]); // The index has been given is not existing or NOT DEFINED in the variable
diff --git a/1-exercises/B-while-loop/exercise.js b/1-exercises/B-while-loop/exercise.js
index b459888f..27dac1d3 100644
--- a/1-exercises/B-while-loop/exercise.js
+++ b/1-exercises/B-while-loop/exercise.js
@@ -6,7 +6,14 @@
 */
 
 function evenNumbers(n) {
-    // TODO
+  // TODO
+  const arr = [];
+  let i = 0;
+  while (i < n) {
+    arr.push(2 * i);
+    i++;
+  }
+  console.log(arr.toString());
 }
 
 evenNumbers(3); // should output 0,2,4
diff --git a/1-exercises/C-while-loop-with-array/exercise.js b/1-exercises/C-while-loop-with-array/exercise.js
index d584cd75..a94b4784 100644
--- a/1-exercises/C-while-loop-with-array/exercise.js
+++ b/1-exercises/C-while-loop-with-array/exercise.js
@@ -5,19 +5,27 @@
 */
 
 const BIRTHDAYS = [
-    "January 7th",
-    "February 12th",
-    "April 3rd",
-    "April 5th",
-    "May 3rd",
-    "July 11th",
-    "July 17th",
-    "September 28th",
-    "November 15th"
+  "January 7th",
+  "February 12th",
+  "April 3rd",
+  "April 5th",
+  "May 3rd",
+  "July 11th",
+  "July 17th",
+  "September 28th",
+  "November 15th",
 ];
 
 function findFirstJulyBDay(birthdays) {
-    // TODO
+  // TODO
+
+  let i = 0;
+  while (i < birthdays.length) {
+    if (birthdays[i].includes("July")) {
+      return birthdays[i];
+    }
+    i++;
+  }
 }
 
 console.log(findFirstJulyBDay(BIRTHDAYS)); // should output "July 11th"
diff --git a/1-exercises/D-do-while/exercise.js b/1-exercises/D-do-while/exercise.js
index f10d0764..d577a850 100644
--- a/1-exercises/D-do-while/exercise.js
+++ b/1-exercises/D-do-while/exercise.js
@@ -8,6 +8,13 @@
 
 function evenNumbersSum(n) {
     // TODO
+    let sum = 0;
+    let i = 0;
+    do {
+        sum += 2 * i;
+        i++;
+    }while (i < n);
+    return sum;
 }
 
 console.log(evenNumbersSum(3)); // should output 6