Give a step-by-step breakdown of each line in this program

Author: Iswanna

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

@@ -25,3 +25,168 @@ console.log(`£${pounds}.${pence}`);
 
 // To begin, we can start with
 // 1. const penceString = "399p": initialises a string variable with the value "399p"
+
+// Answer
+const penceString = "399p"
+// declares a variable penceString and assigns a value "399p" to it.
+
+const penceStringWithoutTrailingP = penceString.substring(
+  0,
+  penceString.length - 1
+);
+// Step-by-step breakdown
+// 1. const
+
+// What it means:
+// const is short for constant.
+// It’s a keyword in JavaScript used to declare a variable — a named place in memory where we store a value.
+
+// What makes it special:
+// Once you assign a value to a const variable, you cannot reassign it later.
+
+// 2. penceStringWithoutTrailingP
+
+// What it is:
+// This is the name of the variable we’re creating.
+
+
+// 3. =
+
+// What it means:
+// The equals sign here means assignment, not comparison.
+// It tells JavaScript: “Store the value on the right-hand side into the variable on the left-hand side.”
+
+// So, penceStringWithoutTrailingP will hold whatever value comes from the code on the right side.
+
+// 4. penceString
+
+// What it is:
+// This is a variable that was created earlier in the code:
+
+// 4. .substring(...)
+
+// What it is:
+// .substring() is a built-in method (a function that belongs to strings) in JavaScript.
+
+// What it does:
+// It extracts a section (or slice) of a string, starting and ending at specific positions (index numbers).
+
+// The first number is where to start (inclusive).
+
+// The second number is where to stop (exclusive, it doesn’t include that index).
+
+// ( 0, penceString.length - 1 )
+
+// These are the arguments (inputs) given to the substring() function.
+
+// Let’s understand each one:
+
+// 0
+
+// This means: “Start from the very first character of the string.”
+// In JavaScript, string positions start counting at 0, not 1.
+
+// penceString.length
+
+// .length is a property (not a function).
+// It gives the number of characters in the string.
+
+// For "399p", penceString.length is 4.
+
+// penceString.length - 1
+
+// This means “one less than the total length.”
+
+// 4 - 1 = 3.
+
+// So we’re telling JavaScript: “Stop right before the last character.”
+
+// Putting it all together:
+// penceString.substring(0, penceString.length - 1) means “Take the text in penceString, start at position 0, and stop right before the last character.”
+// So for "399p", it returns "399" — it removes the final p.
+// The variable penceStringWithoutTrailingP will now contain: "399"
+
+const paddedPenceNumberString = penceStringWithoutTrailingP.padStart(3, "0");
+// Step-by-step breakdown
+// 1. const
+
+// Keyword meaning:
+// const is short for constant.
+// It tells JavaScript that we’re creating a new variable whose value cannot be changed later.
+
+// Why use it here?
+// We only need to store the processed result; we’re not planning to change it again.
+
+//  2. paddedPenceNumberString
+
+// This is the variable’s name.
+
+// 3. =
+
+//  equals sign here is the assignment operator.
+
+// It means “store the result on the right-hand side into the variable on the left-hand side.”
+
+// 4. penceStringWithoutTrailingP
+
+// This is another variable that was defined earlier in the program.
+
+// It holds a string like "399", "50", or "5", after removing the “p” at the end of the original price (like "399p" → "399").
+
+// 5. .padStart(3, "0")
+
+// This is a string method — something you can call on a string to make it do something.
+
+// Let’s break it down further:
+
+// a) The dot (.)
+
+// The dot connects the variable (penceStringWithoutTrailingP) with a method (a built-in action it can perform).
+
+// In English: “Hey JavaScript, take this string and do the padStart operation on it.”
+
+// b) padStart(...)
+
+// This is the method name.
+
+// It “pads” the start (the beginning) of a string with extra characters until it reaches a certain length.
+
+// c) The parentheses (3, "0")
+
+// These are the arguments — pieces of information you pass to the method.
+
+// The first argument (3) means:
+// “Make the string at least 3 characters long.”
+
+// The second argument ("0") means:
+// “If it’s shorter than that, add zeros ("0") at the start.”
+
+// Putting it all together
+const paddedPenceNumberString = penceStringWithoutTrailingP.padStart(3, "0");
+// When JavaScript checks the length, it sees that it’s already 3 characters long, so it doesn’t add any zeros.
+// the result "399" is stored in the variable "paddedPenceNumberString"
+
+const pounds = paddedPenceNumberString.substring(
+  0,
+  paddedPenceNumberString.length - 2
+);
+// paddedPenceNumberString.length means the length of the character "399" is 3.
+// paddedPenceNumberString.length - 2 means 3 - 2 = 1
+// paddedPenceNumberString.substring(0 , 1) means take everything from position 0 up till position 1 exclusive. This will return 3
+// const pounds means store the value 3 inside the variable pounds.
+
+const pence = paddedPenceNumberString
+  .substring(paddedPenceNumberString.length - 2)
+  .padEnd(2, "0");
+// paddedPenceNumberString.length means the length of the character "399" is 3.
+// paddedPenceNumberString.length - 2 means 3 - 2 = 1
+// .substring(paddedPenceNumberString.length - 2) means .substring(1) which means take everything from positon 1 to the end. This returns 99
+// .padEnd(2, "0") means make sure the string has at least two characters. If not, add zeros ("0") at the end. for this exercise, 99..padEnd(2, "0") will return 99
+// so, const pence means variable pence will store the value 99
+
+console.log(`£${pounds}.${pence}`);
+// console meaans terminal and log means print or show this message.
+// `£${pounds}.${pence}` is a literal template which means £3.99
+// so, print £3.99 to the terminal
+
+