London | 26-ITP-Jan | Xuanming Hu | Sprint 1 | Coursework

Sprint-1/1-key-exercises/1-count.js

@@ -4,3 +4,8 @@ count = count + 1;
 
 // Line 1 is a variable declaration, creating the count variable with an initial value of 0
 // Describe what line 3 is doing, in particular focus on what = is doing
+
+// Line 3 is reassigning a new value to the 'count' variable.
+// In JavaScript, '=' is the assignment operator, not a mathematical equals sign. 
+// It first evaluates the expression on the right side (count + 1, which is 0 + 1), 
+// and then assigns that result (1) back to the variable on the left side, updating its value.

Sprint-1/1-key-exercises/2-initials.js

@@ -5,7 +5,7 @@ let lastName = "Johnson";
 // Declare a variable called initials that stores the first character of each string.
 // This should produce the string "CKJ", but you must not write the characters C, K, or J in the code of your solution.
 
-let initials = ``;
-
+let initials = `${firstName[0]}${middleName[0]}${lastName[0]}`;
+console.log(initials);
 // https://www.google.com/search?q=get+first+character+of+string+mdn
 

Sprint-1/1-key-exercises/3-paths.js

@@ -17,7 +17,8 @@ console.log(`The base part of ${filePath} is ${base}`);
 // Create a variable to store the dir part of the filePath variable
 // Create a variable to store the ext part of the variable
 
-const dir = ;
-const ext = ;
-
+const dir = filePath.slice(0, lastSlashIndex);
+const ext = filePath.slice(filePath.lastIndexOf("."));
+console.log(`The dir part of ${filePath} is ${dir}`);
+console.log(`The ext part of ${filePath} is ${ext}`);
 // https://www.google.com/search?q=slice+mdn

Sprint-1/1-key-exercises/4-random.js

@@ -7,3 +7,11 @@ const num = Math.floor(Math.random() * (maximum - minimum + 1)) + minimum;
 // Try breaking down the expression and using documentation to explain what it means
 // It will help to think about the order in which expressions are evaluated
 // Try logging the value of num and running the program several times to build an idea of what the program is doing
+console.log(num);
+// Answer: The variable `num` represents a random whole number between 1 and 100 (inclusive).
+// Breakdown of the expression:
+// 1. Math.random() generates a random decimal number between 0 (inclusive) and 1 (exclusive).
+// 2. (maximum - minimum + 1) calculates the total number of possible integers in our range (which is 100).
+// 3. Multiplying them scales the random decimal to be between 0 and 99.999...
+// 4. Math.floor() rounds that decimal down to the nearest whole number (getting an integer from 0 to 99).
+// 5. Finally, '+ minimum' shifts the starting point up by 1, resulting in a final integer from 1 to 100.

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

@@ -1,2 +1,7 @@
-This is just an instruction for the first activity - but it is just for human consumption
-We don't want the computer to run these 2 lines - how can we solve this problem?
+//This is just an instruction for the first activity - but it is just for human consumption
+//We don't want the computer to run these 2 lines - how can we solve this problem?
+
+// Explanation: 
+// Running this without comments gives a "SyntaxError". 
+// This occurs because the computer tries to read plain English sentences as JavaScript code, which it cannot understand. 
+// Adding '//' turns them into comments that the computer ignores.

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

@@ -1,4 +1,8 @@
 // trying to create an age variable and then reassign the value by 1
 
-const age = 33;
+let age = 33;
 age = age + 1;
+
+// Explanation: 
+// The error is "TypeError: Assignment to constant variable." 
+// This occurs because we used 'const' to declare the 'age' variable. 'const' creates a constant whose value cannot be reassigned after its initial creation.

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

@@ -1,5 +1,8 @@
 // Currently trying to print the string "I was born in Bolton" but it isn't working...
 // what's the error ?
-
-console.log(`I was born in ${cityOfBirth}`);
 const cityOfBirth = "Bolton";
+console.log(`I was born in ${cityOfBirth}`);
+
+// Explanation: 
+// The error is "ReferenceError: Cannot access 'cityOfBirth' before initialization."
+// JavaScript executes code from top to bottom. We tried to print 'cityOfBirth' before we actually declared and initialized it on the next line.

Sprint-1/2-mandatory-errors/3.js

@@ -1,9 +1,13 @@
-const cardNumber = 4533787178994213;
+const cardNumber = "4533787178994213";
 const last4Digits = cardNumber.slice(-4);
-
+console.log(last4Digits);
 // The last4Digits variable should store the last 4 digits of cardNumber
 // However, the code isn't working
 // Before running the code, make and explain a prediction about why the code won't work
 // Then run the code and see what error it gives.
 // Consider: Why does it give this error? Is this what I predicted? If not, what's different?
 // Then try updating the expression last4Digits is assigned to, in order to get the correct value
+
+// Explanation: 
+// The error is "TypeError: cardNumber.slice is not a function."
+// This occurs because the original cardNumber was a Number type. The '.slice()' method only works on Strings and Arrays, not on pure numbers.

Sprint-1/2-mandatory-errors/4.js

@@ -1,2 +1,9 @@
-const 12HourClockTime = "20:53";
-const 24hourClockTime = "08:53";
+const time12Hour = "20:53";
+const time24Hour = "08:53";
+
+console.log(time12Hour);
+console.log(time24Hour);
+
+// Explanation: 
+// The error is a "SyntaxError". 
+// This occurs because it violates JavaScript naming conventions: variable names cannot start with a number.

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

@@ -12,11 +12,12 @@ 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 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 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
-
+// Answer: Lines 1, 2, 7, and 8.
 // e) Describe what the expression Number(carPrice.replaceAll(",","")) is doing - what is the purpose of this expression?
+// Answer: It removes the comma from the string using `replaceAll()`, and then converts that cleaned string into a number type using `Number()`. The purpose is to convert a formatted text string into a valid mathematical number so we can do calculations with it later.

Sprint-1/3-mandatory-interpret/2-time-format.js

@@ -12,14 +12,15 @@ console.log(result);
 // For the piece of code above, read the code and then answer the following questions
 
 // a) How many variable declarations are there in this program?
-
+// Answer: There are 6 variable declarations. (They are: movieLength, remainingSeconds, totalMinutes, remainingMinutes, totalHours, and result).
 // b) How many function calls are there?
-
+// Answer: There is exactly 1 function call (console.log on line 10).
 // c) Using documentation, explain what the expression movieLength % 60 represents
 // https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Arithmetic_Operators
-
+// Answer: The `%` symbol is the remainder (modulo) operator. `movieLength % 60` calculates the leftover seconds that do not fit into a full 60-second minute.
 // d) Interpret line 4, what does the expression assigned to totalMinutes mean?
-
+// Answer: It subtracts the leftover seconds from the total seconds to get a number cleanly divisible by 60, then divides by 60 to find out exactly how many full minutes are in the movie.
 // e) What do you think the variable result represents? Can you think of a better name for this variable?
-
+// Answer: `result` represents the final formatted time string (Hours:Minutes:Seconds). A better, more descriptive name could be `formattedTime` or `movieDurationString`.
 // f) Try experimenting with different values of movieLength. Will this code work for all values of movieLength? Explain your answer
+// Answer: It works for positive whole numbers. However, it won't format single-digit numbers perfectly (e.g., it prints 2:5:9 instead of 02:05:09). Also, it might produce weird results or decimals if we input negative numbers or fractional seconds.

Sprint-1/3-mandatory-interpret/3-to-pounds.js

@@ -25,3 +25,19 @@ console.log(`£${pounds}.${pence}`);
 
 // To begin, we can start with
 // 1. const penceString = "399p": initialises a string variable with the value "399p"
+
+// 2. const penceStringWithoutTrailingP = ... 
+// Removes the last character (the "p") from the string using substring(), leaving just the numbers.
+
+// 3. const paddedPenceNumberString = ...
+// Uses padStart(3, "0") to make sure the string is at least 3 characters long by adding "0"s to the front. 
+
+// 4. const pounds = ...
+// Uses substring() to extract all characters EXCEPT the last two. This isolates the pound value.
+
+// 5. const pence = ...
+// Extracts exactly the last two characters for the pence value using substring(), 
+// and uses padEnd() as a safety measure to ensure it's exactly 2 digits long.
+
+// 6. console.log(...)
+// Uses template literals to piece the pounds and pence back together with a "£" and "." symbol, printing "£3.99".

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