Mandatory errors were fixed and Explained

Author: RomanSanaye

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

@@ -1,2 +1,8 @@
+
 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?
+We don't want the computer to run these 2 lines - how can we solve this problem?
+
+//solution: Simply comment the lines.
+// 1- single line comment like: // example ...
+// 2- multiline comment like : /* a, b, c */
+// comments are for instruction of guidance of who will read our codes, but the computer wont read them.

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

@@ -1,4 +1,10 @@
 // trying to create an age variable and then reassign the value by 1
 
 const age = 33;
-age = age + 1;
+//age = age + 1;
+
+// we can't do that with const variable, because JS locks the reference. 
+// the best choice is to use "let" variable.
+let age2 = 33;
+age2 = age2 + 1; // or age++ if wanna increase by "1";
+console.log(age2);

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

@@ -1,5 +1,9 @@
 // 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}`);
+        //const cityOfBirth = "Bolton";
+
+// the problem is that our variable is not declared when we print it.
+// to make it work, we should declare our "cityOfBirth" variable before we print it.

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

@@ -1,5 +1,14 @@
 const cardNumber = 4533787178994213;
-const last4Digits = cardNumber.slice(-4);
+//const last4Digits = cardNumber.slice(-4);
+let str = cardNumber.toString().slice(-4);
+const last4Digits = Number(str);
+console.log(`${last4Digits} is the last 4 digits of ${cardNumber}`);
+
+//console.log(typeof last4Digits);
+
+// 1- the code is not working because 'slice()' method is not working with numbers.
+// 2- it gives "type error" cardNumber.slice is not a function.
+// 3- my prediction was correct as I studied the slice method and knew it.
 
 // The last4Digits variable should store the last 4 digits of cardNumber
 // However, the code isn't working

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

@@ -1,2 +1,12 @@
+/*
 const 12HourClockTime = "20:53";
-const 24hourClockTime = "08:53";
+const 24hourClockTime = "08:53";
+*/
+// As far as I know we can not start a variable name with a number in JS.
+// Therefore these variables throw error.
+// we can start the name of a variable with letters a-z, A-Z, _ ,and $ . 
+// This is how we correctly name our variables:
+const twelveHourClockTime = "20:53";
+const twenty4HourClockTime = "08:53";
+console.log(`Twelve-hour clock: ${twelveHourClockTime}`);
+console.log(`24-hour clock: ${twenty4HourClockTime}`);