In every programming language variables , conditionals and loops are the most important topic as it’s difficult to write complex algorithms without these

We are done with variables in previous article

So let’s start cover conditional statement and loops here in this article

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Conditional Statements

in javascript or any common programming language we have three type of conditional statements

If Else Statements

if(condition){
  // do this
} else{
  // do this
}

above given code snippet is structure of a if else block here

• if : first scope that will run if condition is true

• condition : boolean expression or a boolean variable

• If condition or variable has the false value then it will run else block

Example

let flag = true; // a boolean variable

if(flag){
  console.log("Value is true"); //output : 'Value is true'    // only this code will run 
  flag = false;
} else{
  console.log("Value is false"); //output : 'Value is false'
  flag = true;
}

It’s second version is with using else if block

if(cond1){
  // code 
}else if( cond2 ){
  //code
}else{
  // code
}

Similar to if-else but has one or more middle blocks with more conditions

example

let marks  = 84

if (marks > 90) {
  console.log("A+");
} else if (marks > 80) {
  console.log("A"); // this blocks gives the output : "A"
} else if (marks > 70) {
  console.log("B");
} else if (marks > 60) {
  console.log("C");
} else if (marks > 50) {
  console.log("D");
} else{
  console.log("Fail");
}

We can also write nested if-else condition ( if - else condition inside another if else block )

Switch Case Statements

now in if else we can use any kind of comparison operators but in Switch Case Statement we only focus on strict equality operator

• As we pass a simple variable to the switch case statement

• then create multiple cases for where we compare value of such variables with different cases using ===

• and if it matches, we run the code for that code

Works similarly as a switch like you pass electricity to all sockets but only one socket passes electricity the one whose switch is one

structure with example

let day = 3;

switch (day){
  case 1 : console.log("Monday");
  break;
  case 2 : console.log("Tuesday");
  break;
  case 3 : console.log("Wednesday"); // only this statement will run 
  break;
  case 4 : console.log("Thursday");
  break;
  case 5 : console.log("Friday");
  break;
  case 6 : console.log("Saturday");
  break;
  case 7 : console.log("Sunday");
  break;
  default: console.log("Invalid day");
}

Assignment : Try running the same code without break; keyword and observe the code

Ternary Operators

Unlike other two conditional statement this one process values on true and false

• or say if-else block without any else if condition

• But it allows nested ternary conditions

used for conditional assignment

Structure

let myVariable = expression ? output1_if_expression_returns_true : else_output2

examples

let age = 25;
let isAllowedToVote = age >= 18 ? true : false;

console.log(isAllowedToVote) // output is true

let age = 31;

let ageStatus = age >= 15 
          ? age > 19 && age <= 29 
            ? "In his twenties"
            : "Not in his twenties" 
          : "child";

console.log(ageStatus) // output is Not in his twenties

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Loops

While coding you stumble upon some problem statement where you to traverse all the numbers or range of given data set from a starting point to end point

in javascript we mainly get 3 loops for performing such actions

For Loop

for(let i = startIndex ; termination_condition ; change_the_value_by ){
  //code 
}

• startIndex : initial value of taken varibale

• termination_condition : loop will run till this condition is satisfied

• change_the_value_by : after each iteration value of taken variable will change by the logic written here

Printing a table of 2 using this

for (let i = 1; i <= 10; i =i+ 1) {
  console.log("2 X " + i + " = " + i * 2);
}

/**
 '2 X 1 = 2'
'2 X 2 = 4'
'2 X 3 = 6'
'2 X 4 = 8'
'2 X 5 = 10'
'2 X 6 = 12'
'2 X 7 = 14'
'2 X 8 = 16'
'2 X 9 = 18'
'2 X 10 = 20'
 */

While loop

let i = startIndex
while(termination_condition){
  //code
  change_the_value_by;
}

Printing a table of 2 using this in reverse order

let i = 10
while(i > 0){
  console.log("2 X " + i + " = " + i * 2);
  // i++; // shorthand for i = i+1
  i--; // shorthand for i = i-1
}
/*
'2 X 10 = 20'
'2 X 9 = 18'
'2 X 8 = 16'
'2 X 7 = 14'
'2 X 6 = 12'
'2 X 5 = 10'
'2 X 4 = 8'
'2 X 3 = 6'
'2 X 2 = 4'
'2 X 1 = 2'
*/

Do While

let i = startIndex;
do{
    // code
  change_the_value_by 
}while(termination_condition)

Printing a table of 2 using this in reverse order

let i = 10
while(i > 0){
  console.log("2 X " + i + " = " + i * 2);
  // i++; // shorthand for i = i+1
  i--; // shorthand for i = i-1
}
/*
'2 X 10 = 20'
'2 X 9 = 18'
'2 X 8 = 16'
'2 X 7 = 14'
'2 X 6 = 12'
'2 X 5 = 10'
'2 X 4 = 8'
'2 X 3 = 6'
'2 X 2 = 4'
'2 X 1 = 2'
*/

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Now we are done with two more important topics conditionals and loops so let’s see in you next article where we will be covering more javascript topics