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Why am I getting infinite loop in JavaScript

I am trying to return the factorial of a provided integer. In this case, for example:

factorialize(num) {
    for (var i = 1;i <= num; i++){
        num*=i;
    }
        return num;
    }
factorialize(5);

I get an infinite loop. Although I understand that this shouldn't give me the correct answer, because my understanding of it would be something like this:

n! = 5 * 1 * 2 * 3 * 4 * 5 = 600

when should it really go:

n! = 1 * 2 * 3 * 4 * 5 = 120

But still, I don't understand why I am getting an infinite loop here?

+3


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9 replies


Let's assume the value of the variable num

is 2

.

  • First cycle:

    for (var i = 1; i <= 2; i++) { //true
   num *= i; //2 = 2 * 1 => 2
}

  • Second loop:

    for (var i = 2; i <= 2; i++) { //true
   num *= i; //2 = 2 * 2 => 4
}

  • Third cycle:

    for (var i = 3; i <= 4; i++) { //true
   num *= i; //4 = 4 * 3 => 12
}

  • Fourth cycle:

    for (var i = 4; i <= 12; i++) { //true
   num *= i; //12 = 12 * 4 => 48
}

The value num

increases exponentially and the value i

increases linearly .

i <= num

the condition will always be met , so you end up with an infinite loop.



enter image description here

Snippet containing the diagram:

var num = {
  x: [1, 2, 3, 4, 5],
  y: [2, 4, 12, 48, 240],
  type: 'scatter',
  name: 'num'
};
var i = {
  x: [1, 2, 3, 4, 5],
  y: [1, 2, 3, 4, 5],
  type: 'scatter',
  name: 'i'
};
var data = [num, i];
Plotly.newPlot('myDiv', data);
      

        
        
        
      

    
<script src="https://cdn.plot.ly/plotly-latest.min.js"></script>
<div id="myDiv" style="width: 480px; height: 400px;">
Run codeHide result


+8


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Your loop is chasing a moving target.

It will end when i

reached num

, but you continue to do num

anymore; in fact i

never reach num

.



As you pointed out, your algorithm is wrong anyway.

function factorialize(num) {
   var result = 1;
   for (var i = 2; i <= num; i++) {
      result *= i;
   }
   return result;
}

console.log(factorialize(0));  // 1
console.log(factorialize(1));  // 1
console.log(factorialize(2));  // 2
console.log(factorialize(3));  // 6
console.log(factorialize(4));  // 24
console.log(factorialize(5));  // 120
+2


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The variable you use in the for loop is the same variable you use to store the multiplication.

This should work:

factorialize(num) {
    var len = num;
    for (var i = 1;i <= len; i++){
        num*=i;
    }
        return num;
    }
factorialize(5);
+1


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This is because you are updating the value dynamically num

. This way, after each iteration, the number gets bigger and bigger, and therefore the value i

will never be greater than the value num

(for values num

greater than 1).

0


source


Because you are changing the value of 'num' every iteration. You must use the third variable to calculate the product.

0


source


You end up with an infinite loop because you are always updating num. You do num = num * i

. Thus, he can never reach the end of the cycle. i

there will never be more num

.

0


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Taking your example:

Before starting 1: num = 5; After starting 1: num = 5; After starting 2: num = 10; After starting 3: num = 30;

According to your condition, the loop will only stop when num is greater than i, which it never will, since you change its value at each iteration by a huge difference.

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here i

never catchnum 

i = 1 num = 5  1 <= 5  //(num = 5*1)
i = 2 num = 5  2 <= 10 //(num = 5*2) 
i = 3 num = 10 3 <= 30 //(num = 10*3)
...
0


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The end condition for is i<=num

always true

, therefore, an infinite loop, because the argument num

keeps increasing with each iteration. The best approach is

function factorialize(num) {
  var res = 1;
  if(num ===0 || num === 1){
    return 1;
	}
   for (var i = 2;i <= num; i++){
      res*=i;
    }
      return res;
    }
factorialize(5);
Run codeHide result


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