Javascript Practice 67: JS Hero - while loop

 

Question: 

Write a function spaces that takes a natural number n and returns a string of n spaces.

Example: spaces(1) should return ' '.

Answer: 

function spaces (num) {

  let mySpaces = '';

  while (num-- > 0)

    mySpaces += ' '; 

  return mySpaces;

};

> declare a function spaces

> it has 1 parameter 'num'

> declare a variable mySpaces

> initialize it with an empty string

> we use a while loop as we need to repeat an action multiple times

> in this case we need to add blank spaces to a string 

> our '''empty spaces string''' will be stored in the variable mySpaces

> blank spaces will be equal to the 'num' parameter, which is fed when the function 'spaces' is called

> while loops have: a condition and a code (loop body) 

> our condition is to ensure that the code should execute as long as the num is greater than 0

> our condition is (num-- > 0)

> our code is: mySpaces += ''

> so if our function is called with the following parameter then how would this while loop work

>> spaces (3)

>> first it will check if 3 > 0; which it is and it will execute the code

>> mySpaces = mySpaces + ' '; the result in variable mySpace will now be ' ' (1 space)

>> then since we have used the num as a counter (num--), the loop will reduce 1 from 3 = 2

>> it will check if 2 > 0; which it is and it will execute the code

>> mySpaces = mySpaces + ' '; the result in variable mySpace will now be '  ' (2 spaces)

>> then since we have used the num as a counter (num--), the loop will reduce 1 from 2 = 1

>> it will check if 1 > 0; which it is and it will execute the code

>> mySpaces = mySpaces + ' '; the result in variable mySpace will now be '   ' (3 spaces)

>> then since we have used the num as a counter (num--), the loop will reduce 1 from 1 = 0

>> it will check if 0 > 0; which it is not and it will only execute the code after the while loop

>> we return the mySpaces variable which will give us the final result