CODEWITHSUNDEEP
javascript
user11586294
user11586294

Reputation:

Algorithm challenge: Repeating a string

just learning JS and am going through Algorithm challenges.

The below code should repeat a string (str) x (num) times.

So for example repeatStringNumTimes('*', 3) should be '***'. The below code does that... but there is an 'undefined' word that appears in the beginning of the output. Why is that?! I've defined all variables... 

function repeatStringNumTimes(str, num) {

    let len = str.length;
    let string;

for (let i = 0; i < num; i++) {

    for (let x = 0; x < len; x++) {

        string += str[x];

    }

}
return string;
}

console.log(repeatStringNumTimes('*', 10));

Upvotes: 1

Views: 129

Answers (4)

User863
User863

Reputation: 20039

Traditional approach using while

const repeatStringNumTimes = (str, num) => {
  let res = str
  while (--num) res += str
  return res
}

console.log(repeatStringNumTimes('*', 10))

Using String.prototype.repeat

const repeatStringNumTimes = (str, num) => str.repeat(num)

console.log(repeatStringNumTimes('*', 10))

Using String.prototype.padStart() or String.prototype.padEnd()

const repeatStringNumTimes = (str, num) => ''.padStart(num, str)

console.log(repeatStringNumTimes('*', 10))

Using Array.prototype.join()

const repeatStringNumTimes = (str, num) => Array(num).join(str)

console.log(repeatStringNumTimes('*', 10))

Upvotes: 0

rs7
rs7

Reputation: 1630

You probably need to declare string:

let string = "";

UPDATE:

That is because of this line: 

string += str[x];

Which equates to:

string = string + str[x]; 
// equivalent to string = undefined + str[x]

You are assigning an undefined string to itself (+ str[x]), if that makes sense.

Upvotes: 0

vp_arth
vp_arth

Reputation: 14982

I've defined all variables

Yes you define it, but not initialize.

Default initalization in javascript is undefined.

So, let a; equals to let a = undefined;
You should initialize your strings with empty string: 

let string = '';

Just a note:

Modern javascript engines have String.prototype.repeat method for that task: 

console.log('*'.repeat(10)); // **********

Upvotes: 3

user11586294
user11586294

Reputation:

Ok so, in order to make this work I added 

let string = "";

I'm not sure why that works though. Any insight from someone more experienced would be greatly appreciated.

Upvotes: 0

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