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Control Statement and loops

Control Statement and loops in javascript


 1)If…Else

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

Example:


var tomorrow = 'rain';

if(tomorrow == 'rain'){
  console.log('take a raincoat');
}else{
  console.log('No need to take a raincoat');
}

output:


PS C:UsersThe-BeastDesktopjavascript Blog> node index.js        
take a raincoat
PS C:UsersThe-BeastDesktopjavascript Blog> 

Example:


var tomorrow = 'no rain';

if(tomorrow == 'rain'){
  console.log('take a raincoat');
}else{
  console.log('No need to take a raincoat');
}

output:


PS C:UsersThe-BeastDesktopjavascript Blog> node index.js        
No need to take a raincoat
PS C:UsersThe-BeastDesktopjavascript Blog>

2) switch Statement

Evaluates an expression, matching the expression’s value to a case clause, and executes statements associated with that case.
1st without a break statement.

Example: Find the Area of circle, triangle, and rectangle?

 

var area = "circle" ;
var PI = 3.142, l=6, b=5, r=4;

if(area == "circle"){
  console.log("the area of the circle is : " + PI*r**2);
}else if(area == "triangle"){
  console.log("the area of the triangle is : " + (l*b)/2);
}else if(area == "rectangle"){
  console.log("the area of the rectangle is : " + (l*b));
}else{
  console.log("please enter valid data");
}

output:


PS C:UsersThe-BeastDesktopjavascript Blog> node index.js        
the area of the circle is : 50.272
PS C:UsersThe-BeastDesktopjavascript Blog> 

using break statement

Example:


var area = "circle" ;
var PI = 3.142, l=6, b=5, r=4;

switch(area){
  case 'circle': 
    console.log("the area of the circle is : " + PI*r**2);
    break;

  case 'triangle':
    console.log("the area of the triangle is : " + (l*b)/2);
    break;

  case 'rectangle':
    console.log("the area of the rectangle is : " + (l*b));
    break;

  default:
    console.log("please enter valid data");
}   

output:


PS C:UsersThe-BeastDesktopjavascript Blog> node index.js        
the area of the circle is : 50.272
PS C:UsersThe-BeastDesktopjavascript Blog> 

break

Terminates the current loop, switch, or label statement and transfers program control to the statement following the terminated statement.

continue

Terminates execution of the statements in the current iteration of the current or labeled loop, and continues execution of the loop with the next iteration.

3)While Loop Statement

The while statement creates a loop that executes a specified statement as long as the test condition evaluates to true.

Example:


var num=0;

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

output:


PS C:UsersThe-BeastDesktopjavascript Blog> node index.js        
0
1
2
3
4
5 
6 
7 
8 
9 
10
PS C:UsersThe-BeastDesktopjavascript Blog> 

4)Do-While Loop Statement

The do…while loop is similar to the while loop except that the condition check happens at the end of the loop. This means that the loop will always be executed at least once, even if the condition is false.

Example:


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

output:


PS C:UsersThe-BeastDesktopjavascript Blog> node index.js        
20
PS C:UsersThe-BeastDesktopjavascript Blog> 

5)For Loop

Looping in programming languages is a feature that facilitates the execution of a set of instructions/functions repeatedly while some condition evaluates to true. A Loop executes the sequence of statements many times until the stated condition becomes false.

Example:


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

output:


PS C:UsersThe-BeastDesktopjavascript Blog> node index.js        
0
1 
2 
3 
4 
5 
6 
7 
8 
9 
10
PS C:UsersThe-BeastDesktopjavascript Blog> 

What are truthy and falsy values in Javascript?

we have a total of 5 falsy values in javascript.

0,” “,undefined,null,NaN,false.

Example:



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

output:


PS C:UsersThe-BeastDesktopjavascript Blog> node index.js        
OMG, we loss the game 
PS C:UsersThe-BeastDesktopjavascript Blog> 

Example:



if(score = 50){
    console.log("Yay, We won the game ");
}else{
    console.log("OMG, we loss the game ");
}

output:


PS C:UsersThe-BeastDesktopjavascript Blog> node index.js        
Yay, We won the game 
PS C:UsersThe-BeastDesktopjavascript Blog> 

watch the video:https://youtu.be/KGkiIBTq0y0

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