Fix: correct answers for questions a and b in 1-percentage-change.js

Author: Samual-Hu

Sprint-1/3-mandatory-interpret/1-percentage-change.js

@@ -12,9 +12,9 @@ console.log(`The percentage change is ${percentageChange}`);
 // Read the code and then answer the questions below
 
 // a) How many function calls are there in this file? Write down all the lines where a function call is made
-// Answer: There are 2 function calls in total. They are both `Number()` and are located on lines 4 and 5.
+// Answer: There are 5 function calls in total. They are located on lines 4, 5, and 10.
 // b) Run the code and identify the line where the error is coming from - why is this error occurring? How can you fix this problem?
-// Answer: The error comes from line 5. It occurs because we are trying to reassign a value to `priceAfterOneYear`, which was originally declared as a `const`. To fix it, change `const` to `let` on line 2.
+// Answer: The error comes from line 4. Since JavaScript executes from top to bottom, it crashes on line 4 because we are trying to reassign a new value to `carPrice`, which was originally declared as a `const`. To fix it, change `const` to `let` on lines 1 and 2.
 // c) Identify all the lines that are variable reassignment statements
 // Answer: Lines 4 and 5.
 // d) Identify all the lines that are variable declarations

Sprint-2/1-key-errors/0.js

@@ -1,13 +1,18 @@
 // Predict and explain first...
 //  =============> write your prediction here
-
+// It will crash with a SyntaxError. We can't use 'let' to declare 'str' because 'str' is already taken by the function parameter.
 // call the function capitalise with a string input
 // interpret the error message and figure out why an error is occurring
-
+/* I commented this out so it doesn't crash:
 function capitalise(str) {
   let str = `${str[0].toUpperCase()}${str.slice(1)}`;
   return str;
 }
-
+*/
 // =============> write your explanation here
+//The error confirms "str has already been declared". Function parameters act as local variables, creating a naming conflict with `let str`.
 // =============> write your new code here
+function capitalise(str) {
+  return `${str[0].toUpperCase()}${str.slice(1)}`;
+}
+console.log(capitalise("hello"));

Sprint-2/1-key-errors/1.js

@@ -2,9 +2,9 @@
 
 // Why will an error occur when this program runs?
 // =============> write your prediction here
-
+// It will crash for two reasons. 1. Trying to log a local variable 'decimalNumber' outside its function. 2. Trying to re-declare the parameter 'decimalNumber' using 'const' inside the function.
 // Try playing computer with the example to work out what is going on
-
+/* Commented out broken code:
 function convertToPercentage(decimalNumber) {
   const decimalNumber = 0.5;
   const percentage = `${decimalNumber * 100}%`;
@@ -13,8 +13,12 @@ function convertToPercentage(decimalNumber) {
 }
 
 console.log(decimalNumber);
-
+*/
 // =============> write your explanation here
-
+// 'decimalNumber' is scoped to the function, so console.log outside can't see it (ReferenceError). Inside, re-declaring the parameter with 'const' causes a SyntaxError. Also, the function was never actually called.
 // Finally, correct the code to fix the problem
 // =============> write your new code here
+function convertToPercentage(decimalNumber) {
+  return `${decimalNumber * 100}%`;
+}
+console.log(convertToPercentage(0.5));

Sprint-2/1-key-errors/2.js

@@ -4,17 +4,22 @@
 // this function should square any number but instead we're going to get an error
 
 // =============> write your prediction of the error here
-
+// Syntax error. We put a hardcoded number '3' where a parameter name (like 'num') should be.
+/* Commented out the broken code so it doesn't crash:
 function square(3) {
     return num * num;
 }
-
+*/
 // =============> write the error message here
-
+// SyntaxError: Unexpected number
 // =============> explain this error message here
-
+// Function definitions require variable names as parameters to act as placeholders, not literal values.
 // Finally, correct the code to fix the problem
 
 // =============> write your new code here
-
+function square(num) {
+  return num * num;
+}
+console.log(square(3)); 
+console.log(square(4));
 

Sprint-2/2-mandatory-debug/0.js

@@ -1,14 +1,19 @@
 // Predict and explain first...
 
 // =============> write your prediction here
-
+//It will print "320", followed by "The result... is undefined". The function lacks a return value.
+/* Commented out the broken code:
 function multiply(a, b) {
   console.log(a * b);
 }
 
 console.log(`The result of multiplying 10 and 32 is ${multiply(10, 32)}`);
-
+*/
 // =============> write your explanation here
-
+// `console.log` just prints to the screen. Without a `return` statement, the function evaluates to `undefined`, which gets injected into the template literal.
 // Finally, correct the code to fix the problem
 //  =============> write your new code here
+function multiply(a, b) {
+  return a * b;
+}
+console.log(`The result of multiplying 10 and 32 is ${multiply(10, 32)}`);

Sprint-2/2-mandatory-debug/1.js

@@ -1,13 +1,19 @@
 // Predict and explain first...
 //  =============> write your prediction here
-
+// It will print "undefined". The 'return;' statement stops the function immediately before it even looks at 'a + b'.
+/* Commented out the broken code:
 function sum(a, b) {
   return;
   a + b;
 }
 
 console.log(`The sum of 10 and 32 is ${sum(10, 32)}`);
-
+*/
 // =============> write your explanation here
+// The 'return' keyword instantly exits the function. Since nothing is attached to it, it returns 'undefined'. The 'a + b;' line is dead code that never gets executed.
 // Finally, correct the code to fix the problem
 //  =============> write your new code here
+function sum(a, b) {
+  return a + b;
+}
+console.log(`The sum of 10 and 32 is ${sum(10, 32)}`);

Sprint-2/2-mandatory-debug/2.js

@@ -2,7 +2,8 @@
 
 // Predict the output of the following code:
 // =============> Write your prediction here
-
+// It will always print "3" for every log. The function ignores the numbers we pass in and blindly uses the global 'num' (103).
+/* Commented out the broken code:
 const num = 103;
 
 function getLastDigit() {
@@ -12,13 +13,22 @@ function getLastDigit() {
 console.log(`The last digit of 42 is ${getLastDigit(42)}`);
 console.log(`The last digit of 105 is ${getLastDigit(105)}`);
 console.log(`The last digit of 806 is ${getLastDigit(806)}`);
-
+*/
 // Now run the code and compare the output to your prediction
 // =============> write the output here
+// The last digit of 42 is 3
+// The last digit of 105 is 3
+// The last digit of 806 is 3
 // Explain why the output is the way it is
 // =============> write your explanation here
+// The function lacks a parameter in its definition. Therefore, it ignores the arguments (42, 105, 806) and always falls back to the globally defined 'num' which is 103.
 // Finally, correct the code to fix the problem
 // =============> write your new code here
-
+function getLastDigit(number) {
+  return number.toString().slice(-1);
+}
+console.log(`The last digit of 42 is ${getLastDigit(42)}`);
+console.log(`The last digit of 105 is ${getLastDigit(105)}`);
+console.log(`The last digit of 806 is ${getLastDigit(806)}`);
 // This program should tell the user the last digit of each number.
 // Explain why getLastDigit is not working properly - correct the problem