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 2 function calls in total. They are both `Number()` and are located on lines 4 and 5.
 // 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.
 // 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".