10feb

Author: INDRESH-009

.DS_Store

@@ -44,3 +44,172 @@ for(let i=3;i<=terms;++i){  //iterating form term 3
     nextterm = t1+t2;       //now add the new 2 preceding terms 
 }
 
+
+//ARRAYS
+
+//arrays - They are a datastructure which grps similar kinds if data
+// declaring a  array in js
+let ages = [12,13,14,56,34,67];
+//printing only even ages from the array
+for(let i=0;i<=ages.length;i++){
+    ages[i]%2==0 ? console.log(ages[i]) : "";
+}
+
+//write a code to pint the biggest number in an array
+let max = 0;
+for(let i=0;i<ages.length;i++){
+    ages[i]>max ? max = ages[i] : "";
+}
+console.log(`The maximum number is ${max}`);
+
+//reverse an array
+let num=[1,2,3,4,5];
+let revnum=[];
+for(let i=0;i<num.length;i++){
+    revnum[(num.length-1)-i]=num[i];
+}
+console.log(`the reversed array is ${revnum}`);
+
+
+//OBJECTS
+
+//print only the male candidates from a complex objects
+// here we are using object of arrays and to acces those array elements in the object we use the .(dot) operator
+let users={
+    firstname:["indresh","rohan","radha","rama","shiva"],
+    gender:["male","male","female","female","male"]
+}
+for(let i=0;i<users.firstname.length;i++){
+    users.gender[i]=="male"?console.log(users.firstname[i]):"";
+}
+
+//using array of objects print only the male candidates above age 18 from a complex objects
+let userinfo = [
+    {
+        username:"indresh",
+        gender:"male",
+        metadata:{
+            phone:123456789,
+            address:"asdfgg",
+            age:20,
+        }
+    },
+    {
+        username:"shakthi",
+        gender:"female",
+        metadata:{
+            phone:12356789,
+            address:"asdg",
+            age:22,
+        }
+    },
+    {
+        username:"rohan",
+        gender:"male",
+        metadata:{
+            phone:2356789,
+            address:"dfgg",
+            age:10,
+        }
+    }
+]
+for(let i=0;i<userinfo.length;i++){
+    userinfo[i]["gender"]=="male" && userinfo[i]["metadata"]["age"]>18 ? console.log(`male user above 18 is ${userinfo[i]["username"]}`):"";
+}
+
+//FUNCTIONS
+// functions let you abstract out logic out of your program
+// They take argument as input and return value as an output
+//we can think of them as independent program that is supposed to do something when given an input
+//functions can take other functions as input this is called callbacks
+
+
+//write a function to calculate sum of 2 numbers , let  a and b be the parameters and call the funvction with the arguments 12 and 34
+function sum(a,b){
+    let ans = a+b;
+    return ans;
+}
+let sum1 = sum(12,34);
+console.log(sum1);
+
+//creating a function that takes input of 2 numbers and the oprator to provide the solution for the arithematic expression
+function arithmatic(a,b,type){
+    if(type == "+"){
+        return a+b;
+    }
+    else if(type == "-"){
+        return a-b;
+    }
+}
+console.log(arithmatic(12,23,'+'));
+//In the above codebase we directly used the arithematic operations in the conditional stetements itelf.
+
+
+//In the below codebase we are trying to use 2 differnce seperate functions to calculate sum and difference but we use condotional statement just to call those 2 function based on the type of operation user needs to perform like sum or difference
+function calc(a,b,type){
+    if(type == "+"){
+        return sum(a,b);
+    }
+    else if(type == "-"){
+        return difference(a,b);
+    }
+}
+function sum(a,b){
+    return a+b;
+}
+function difference(a,b){
+    return a-b;
+}
+console.log(calc(10,10,"-"));
+
+
+//now instead of using all these conditional statements we are going to use these functins as an argument and this is called callbacks
+
+//here we are giving functions add and sub as a parameter and based on the input the fn is called
+
+//Callbacks functions can be useful only if the 2 functions viz the function viz calling and the function viz called both have same parameters. Callbacks are not used at places where functions have different parameters
+function calculator(num1,num2,operationfn){
+    let ans = operationfn(num1,num2);
+    return ans;
+}
+function add(num1,num2){
+    return num1+num2;
+}
+function sub(num1,num2){
+    return num1-num2;
+}
+console.log(calculator(10,20,sub));
+
+
+//another example of callback function can be understood using setTimeout function
+
+//function to greet someone
+function greet(){
+    console.log("hello world");
+}
+setTimeout(greet,3*1000);
+console.log(greet); //calling greet function
+
+
+//This setTimeout is a function that takes 2 arguments , one is the function it needs to execute and teh other is the time it shd wait ir freez before executing that function. Here 3*1000 - is 3 sec so it means wait for 3 sec before executing the greet function 
+
+
+//basically if u run this program we can see that greet function is executed only after 3 sec of running the program. so here
+
+//setTImeot is a fuction that takes 2 arguments where one of the argument is a function. This is called callbacks
+
+
+
+//Assignment 1
+// Question1 - create a counter in js that counts from 30 to 0
+// Question2 - calculate the time it takes between the setTimeout call and the inner fuction actually running
+// Question3 - create a terminal clock (HH:MM:SS)
+function counter(){
+    for(let i=30;i>0;i--){
+        console.log(i);
+        setTimeout(counter,1000);
+    }
+}
+
+console.log(counter);
+

js_notes/basic-q.js

@@ -15,7 +15,7 @@ for(let j=0;j<=10;j++){
     //if you dont have any else block you still have to complete the syntax using "" as above 
 }
 //using while loop
-let num = 0;
+let num = 0;        
 while(num<=10){
     num%2==0 ? console.log(num) : ""
     num++;
@@ -50,6 +50,17 @@ for(let i=1;i<=2;i++){
     }
 }
 
+/* why are pattern important 
+1. enhances thinking and problem solving skills 
+
+How to approach solving these pattern questions 
+1. Run the outer for loop the no.of times of rows / no.of lines 
+    no.of lines = no.of rows = no.of times the outer loop will run
+2. Identify for every row number how many columns are there.
+3. Undertand the type of elements in the  column like * or numbers etc.. 
+
+*/
+
 
 
 //Print a pattern if starts using nested loops 
@@ -222,14 +233,16 @@ for(let i=1;i<=rows;i++){   //outerloop for no.of rows
     console.log(pattern);
 }
 
+//HOW TO GET USER INPUT FROM TERMINAL IN JS :
+//First, you need to import the readline module:
 const readline = require('readline');
-
+//Then, create an interface to read input from the user:
 const rl = readline.createInterface({
     input: process.stdin,
     output: process.stdout
 });
-
+//Now, you can use the question() method to prompt the user for input:
 rl.question("Enter something: ", function(userInput) {
     console.log("You entered:", userInput);
-    rl.close();
+    rl.close(); //Finally, don't forget to close the interface after reading the input to avoid memory leaks:
 });