📔 Day 3

Conditionals

Conditional statements are used for make decisions based on different conditions. By default , statements in JavaScript script executed sequentially from top to bottom. If the processing logic require so, the sequential flow of execution can be altered in two ways:

Conditions can be implementing using the following ways:

If

In JavaScript and other programming languages the key word if is to used check if a condition is true and to execute the block code. To create an if condition, we need if keyword, condition inside a parenthesis and block of code inside a curly bracket({}).

// syntax
if (condition) {
  //this part of code runs for truthy condition
}

Example:

let num = 3
if (num > 0) {
  console.log(`${num} is a positive number`)
}
//  3 is a positive number

As you can see in the condition example above, 3 is greater than 0, so it is a positive number. The condition was true and the block of code was executed. However, if the condition is false, we won’t see any results.

let isRaining = true
if (isRaining) {
  console.log('Remember to take your rain coat.')
}

The same goes for the second condition, if isRaining is false the if block will not be executed and we do not see any output. In order to see the result of a falsy condition, we should have another block, which is going to be else.

If Else

If condition is true the first block will be executed, if not the else condition will be executed.

// syntax
if (condition) {
  // this part of code runs for truthy condition
} else {
  // this part of code runs for false condition
}
let num = 3
if (num > 0) {
  console.log(`${num} is a positive number`)
} else {
  console.log(`${num} is a negative number`)
}
//  3 is a positive number

num = -3
if (num > 0) {
  console.log(`${num} is a positive number`)
} else {
  console.log(`${num} is a negative number`)
}
//  -3 is a negative number
let isRaining = true
if (isRaining) {
  console.log('You need a rain coat.')
} else {
  console.log('No need for a rain coat.')
}
// You need a rain coat.

isRaining = false
if (isRaining) {
  console.log('You need a rain coat.')
} else {
  console.log('No need for a rain coat.')
}
// No need for a rain coat.

The last condition is false, therefore the else block was executed. What if we have more than two conditions? In that case, we would use else if conditions.

If Else if Else

On our daily life, we make decisions on daily basis. We make decisions not by checking one or two conditions instead we make decisions based on multiple conditions. As similar to our daily life, programming is also full of conditions. We use else if when we have multiple conditions.

// syntax
if (condition) {
     // code
} else if (condition) {
   // code
} else {
    //  code

}

Example:

let a = 0
if (a > 0) {
  console.log(`${a} is a positive number`)
} else if (a < 0) {
  console.log(`${a} is a negative number`)
} else if (a == 0) {
  console.log(`${a} is zero`)
} else {
  console.log(`${a} is not a number`)
}
// if else if else
let weather = 'sunny'
if (weather === 'rainy') {
  console.log('You need a rain coat.')
} else if (weather === 'cloudy') {
  console.log('It might be cold, you need a jacket.')
} else if (weather === 'sunny') {
  console.log('Go out freely.')
} else {
  console.log('No need for rain coat.')
}

Switch

Switch is an alternative for if else if else else. The switch statement starts with a switch keyword followed by a parenthesis and code block. Inside the code block we will have different cases. Case block runs if the value in the switch statement parenthesis matches with the case value. The break statement is to terminate execution so the code execution does not go down after the condition is satisfied. The default block runs if all the cases don’t satisfy the condition.

switch(caseValue){
  case 1:
    // code
    break
  case 2:
   // code
   break
  case 3:
   // code
   break
  default:
   // code
}
let weather = 'cloudy'
switch (weather) {
  case 'rainy':
    console.log('You need a rain coat.')
    break
  case 'cloudy':
    console.log('It might be cold, you need a jacket.')
    break
  case 'sunny':
    console.log('Go out freely.')
    break
  default:
    console.log(' No need for rain coat.')
}

// Switch More Examples
let dayUserInput = prompt('What day is today ?')
let day = dayUserInput.toLowerCase()

switch (day) {
  case 'monday':
    console.log('Today is Monday')
    break
  case 'tuesday':
    console.log('Today is Tuesday')
    break
  case 'wednesday':
    console.log('Today is Wednesday')
    break
  case 'thursday':
    console.log('Today is Thursday')
    break
  case 'friday':
    console.log('Today is Friday')
    break
  case 'saturday':
    console.log('Today is Saturday')
    break
  case 'sunday':
    console.log('Today is Sunday')
    break
  default:
    console.log('It is not a week day.')
}

// Examples to use conditions in the cases

let num = prompt('Enter number');
switch (true) {
  case num > 0:
    console.log('Number is positive');
    break;
  case num == 0:
    console.log('Numbers is zero');
    break;
  case num < 0:
    console.log('Number is negative');
    break;
  default:
    console.log('Entered value was not a number');
}

Ternary Operators

Another way to write conditionals is using ternary operators. We have covered this in other sections, but we should also mention it here.

let isRaining = true
isRaining
  ? console.log('You need a rain coat.')
  : console.log('No need for a rain coat.')

🌕 You are extraordinary and you have a remarkable potential. You have just completed day 3 of 30 days js and you are three steps a head in to your way to greatness. Now do some exercises for your brain and for your muscle memory too. #happy_learning