JavaScript Control Statements & Loops

The Article Conduct Below Topic

• If. Else loop

• Switch Statement

• While Loop

• Do-While Loop

• For Loop

Practise

If .... Else Loop

• The if statement executes a statement if a specified condition is truthy. If the condition is false, another statement can be executed.

Example-1

• write a program that works out whether a given year is a leap year or not

• a leap year has 366

• normal year 365

• leap divide by 4 then === leap year

• not divide by 4 and divide by 100 exactly then === not leap year

• if exactly divide by 400 === leap year

var year = 2020;

if (year % 4 === 0) {

    if (year % 100 === 0) {

        if(year % 400 === 0)
        {
           console.log("this is leap year");
        }
        else
        {
           console.log("this is not leap year");
        }   
    }
    else
    {
    console.log("this is leap year");
    }
}
else
{
  console.log("this is not leap year");
}

OUTPUT

Example-2

• What are truthy and falsy values in Javascript?

• we are total falsy value = 0 || '' || undefined || null || Nan

• if you put a falsy value in the condition then always print else part

    ----------------------------------------
  
    if (score = 0) {
        console.log("Yay, We won the game ");
    } else {
        console.log("OMG, we loss the game ");
    }
    -----------------------------------------
    if (score = 0) {
        console.log( " We loss the game ");
    } else {
        console.log(" we win the game ");
    }
    ----------------------------------------
    if (undefined) {
        console.log( " We loss the game ");
    } else {
        console.log(" we win the game ");
    }
    ----------------------------------
    if (null) {
        console.log( " We loss the game ");
    } else {
        console.log(" we win the game ");
    }
    -----------------------------------
  

  Conditional Operator

• 

• Example-3

  • is only one in js who can take 3 operands(5 + 20 here 5,20)

  • syntax == variableName = (condition) ? value1:value2

  • it's a short form of if...else

    //if.....else

     var age = 19;

     if (age >= 18) {
         console.log("you are elegible to vote");
     } else {
         console.log("you are not elegible to vote");
     }

    //ternary form

     var age = 17;
     console.log(age >= 18 ? "you can vote" : "you cant vote");

Switch Statement

• Evaluates an expression, matching the expression's value to a case clause, and executes statements associated with that case.

• find the area of the circle, triangle and rectangle. through if...else if...else

  

• While Loop

• while statements create a loop that executes as specified statement as long as the test condition evaluates to true

//infinet loop
 var num = 10;
 while (num <= 10) {
     console.log(num);
 }

var num = 0;
while (num <= 10) {
    console.log(num);
    num++
}

//block scope 
var num = 20;
//block scope 
while(num <= 10){
console.log(num); 
num++

• while the loop first checks the condition and then goes to the scope

• just like here, condition will be false and while the loop don't go in scope and we don't get output

Do-While Loop

• do while loop is one problem it gives at least one output then it gives the condition is wrong

var num = 20;
do {
    debugger;
    console.log(num);
    num++;
} while (num <= 10);

For Loop

• the better and short version of while loop & do...while loop

• 

•            for (var num = 0; num <= 10; num++){
                 console.log(num);
             }
  

  for loop debugging

  1. for the first time, num will be initialised and checked condition and print

  2. then after printing its directly goes to num++ then checks the condition and then print