将数组值赋给变量

Question

I came across a problem which I did manage to solve but I honestly do not understand how this works.

var array = [3, 6, 2, 56, 32, 5, 89, 32];
var largest = 0;
//My code
for (var i = 0; i < array.length; i++) {
    if (array[i] > largest) {
        largest = array[i];
    }
}

console.log(largest);

How does my array assign a value to my variable within the if statement?

Why does this version not work?

array[i] = largest;

I'm very new to programming and I believe that understanding fundamental things as small as this can help many beginners become competent programmers.

Answer 1

if(array[i] > largest) {
           largest = array[i];
        }

array[i] is 3 and largest is 0 then if condition passes and

largest = array[i];

assign value right to left now the largest value is 3 .

so next cycle array[i] is 6 so next 6 > 3 true , it will again change the largest to 6 .

like it will give you largest number.

Answer 2

I think you are mistaking the assignment statement in programming with the equality statement in mathematics.

Assignment vs Equality

In your code, when you say largest = array[i] you are assigning to the variable 'largest' the value of the element on the ith position of the array. Notice here that the array is not changing any of its values in this assignment.

On the other hand, array[i] = largest would try to assign to the ith position on the array the present value of the variable 'largest'.

Answer 3

This code is trying to calculate the largest value in an array of values..

Doing

array[i] = largest;

would modify the input itself which is undesired... you need to find the largest value from the given input.. and not modify the given input location to some largest value.

That is why

largest = array[i] 

is correct.

Answer 4

When you assign a value to a variable, the variable has to be on the left of the assignment operator (the equals sign "=").

This way has the variable on the left:

largest = array[i];

It puts the array[i] value into the largest variable, and so it works.

This way is backwards:

array[i] = largest;

It puts the largest value into the array[i] element, and your array ends up with a bunch of zeros in it.

Answer 5

I know this is an old thread, but i've this issue today and want to help others developers with proper source of knowledge, comming directly from Kyle Simpson.

You don't know JS

Operator assignment has his own way to work. It calculate the statement of the right "=" to later asign it, to the left. This is very important to know how does it work.

Example:

var array = [3, 6, 2, 56, 32, 5, 89, 32];
var largest = 0;
//My code
for (var i = 0; i < array.length; i++) {
    if (array[i] > largest) {
        largest = array[i];
    }
}

console.log(largest);

Here, largest = array[i];

JS, is calculate the statement of the right and assing to the left

So have fun with the book and play.