beginner javascript for loop puzzle

Question

I'm new at javascript was wondering why I got four return values:

for(i=0; i < 10; i++) {
    i = i * i;
    console.log(i);
}
// 0
// 1
// 4
// 25

You changed the value of i upon assignment, therefore shortening the loop. — StackSlave
– StackSlave, Commented Mar 14, 2018 at 1:42
Quick note: You're logging 4 values to the console, not getting 4 return values. There's an important distinction there: a return value is a value returned from a function call. — sheeldotme
– sheeldotme, Commented Mar 14, 2018 at 1:56
I suppose I expected more iterations, but now that it was explained the answer was pretty obvious. — Patrick
– Patrick, Commented Mar 14, 2018 at 3:41

Jesse · Accepted Answer · 2018-03-14 01:43:56Z

3

Because you are setting the value of i inside your loop.

Initially i = 0; Prints 0x0 = 0; i = 0

Next iteration i = 1; Print 1x1 = 1; i = 1

Next iteration i = 2; Print 2x2 = 4; i = 4

Next iteration i = 5; Print 5x5 = 25; i = 25

i is now greater than 10 and therefore loop exit condition is met.

answered Mar 14, 2018 at 1:43

Jesse

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1 Comment

Patrick Over a year ago

That's what I suspected while I was away from the computer and giving it some thought. Thanks for clearing that up!

Ele · Accepted Answer · 2018-03-14 01:49:37Z

1

Execute this snippet to get a little explanation:

var iterations = ['First', 'Second', 'Third', 'Fourth']
var j = 0;
for (i = 0; i < 10; i++) {
  var iteration = iterations[j++];
    console.log(`${iteration} iteration with i = ${i} and multiplying ${i} x ${i} =`, i * i);
  i = i * i;

}
console.log(`The for-loop ends because i = ${i} > 10`);

.as-console-wrapper { max-height: 100% !important; top: 0; }

answered Mar 14, 2018 at 1:49

Ele

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Comments

Karl · Accepted Answer · 2018-03-14 01:46:04Z

0

There is an error in the logic of your loop. Since the loop sets the value of i to the product of itself i is repeatedly increasing with each iteration of the loop:

i = i * i;

It makes i greater then 10 (in your example 25) and terminates the loop. If you created some variable, say j as what is set to the product of i * i, it would loop 10 times. Something like this:

for(i=0; i < 10; i++) {
    var j = i * i;
    console.log(j);
}

answered Mar 14, 2018 at 1:46

Karl

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Comments

Qudus Bashiru · Accepted Answer · 2020-12-02 07:25:05Z

0

The loop breaks because of the prior condition you set in your for statement; "i < 10". By assigning a new value to i in "i = i * i" overrides the incremental value "i++" you provided the for loop. To correct this, assign the value from product of "i * i" to a different variable name such as "s = i * i" and you can get your loop to complete without any break.

answered Dec 2, 2020 at 7:25

Qudus Bashiru

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